Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
SECURITY FEATURE FOR PRINTED PRODUCTS
FIELD OF THE INVENTION
The invention relates generally to a security feature for printed products. In
particular, the present
invention provides a printed product and method of printing/metallization to
produce visible
print/image in registration with metallization, for use in printed security
documents including but not
limited to driver's licenses, passports, and banknotes.
BACKGROUND
Security documents and printed products such as identification cards, data
pages, driver's licenses,
passports and banknotes may include one or more images or elements formed by
printing or applying a
printed image. For example, a security document in the form of an
identification card, a driver's license
or personal identification sheet of a passport may be made of a thermoplastic
substrate and may bear
an image comprising a security design feature that is printed onto the
thermoplastic substrate.
Additional features such as metallization may increase the difficulty of
copying the security design
feature.
Metallization by PVD (physical vapor deposition) or chemical deposition is
common in the commercial
world. A flood coat comprising a thin metal layer is applied on the surface of
polymers to use as a vapor
barrier. Selective or pattern metallization is also used for commercial
purposes, especially in decorative
packaging. This is commonly achieved in the following ways.
1. Pattern etching
a. Chemical etching by caustic solution after mask is applied
b. Print a concentrated caustic solution over metallized surface followed by a
wash-up
2. Surface treatment before metallization
a. Print thin oil layer which prevents metal from adhering
The pattern etching uses a corrosive material which must be removed from the
polymer. The process will
be quite expensive due to the nature of the chemicals used.
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The surface treatment process uses oil over the polymer surface b. It is
difficult to remove the oil
completely after metallization. The contamination would interfere with the
process use for card/data
page manufacturing.
Vast Films Ltd applies selective or pattern metallization by a different
process (U520180282551A1). A
release agent is applied to the surface of a transparent film by a
flexographic or other suitable process,
forming a negative image. After the release agent dries, a flood metallization
is applied over the coated
film. The release agent is removed after metallization to obtain the final
metalized film ¨ the positive
image.
As taught in U520180282551, the release agent comprises a polymer such as PVP
or PVOH or a copolymer
thereof that is soluble in water and/or alcohol and is solid at temperatures
about 50 C. The release agent
may further comprise a dye and an anti-blocking agent comprising silica. The
release agent is removed
by washing with water and/or alcohol. This may be achieved by passing the film
through a tank, or by
spraying. After washing, the film may be dried by, for example, an air knife
or hot air.
There is teaching in the prior art in respect of a security device with a
reflective surface at a first side of a
transparent film and an opaque surface at the second side. However, the
process used to achieve such
security device may be complicated and/or it may be difficult to achieve a
perfect registration between
the image/pattern on the two sides.
For example, DE102017011917A1 to Hoffm(Iller discloses a method for producing
a multilayer film
security element. In Hoffrniiller's process, the printing of a colour motif
takes place first, followed by
application of a water-soluble coating and metallization. The registration of
the colour motif to water-
soluble coating is dictated by the printer. For example, the color motif may
be printed on the first print
unit of a printer and the water-soluble coating may be printed on the second
unit to achieve tight
registration. The unit-to-unit mechanical tolerance of the press will make it
more difficult for the colour
motif and coating to be in perfect registration.
U520090220750A1 to Hill discloses partial printing of a substrate using
metallization. Hill's invention
uses four different methods to produce a device.
1. Solvent etch: Harsh solvent is used to etch both colour motif sits at the
bottom of the etch and
the metal sits at the top of the etch. The process will be costly and
environmentally not too
friendly due to the nature of chemicals involved.
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2. Water activated stencil method: Thick stencil layer is used for this
application as a mask.
Metallization form discontinuities at the edge of the thick stencil. The
process is too complicated
and the using thicker stencil would not give high resolution image (>1200dpi).
3. Release layer stencil method: A release layer is printed on the
substrate followed by a colour motif
and metallization. The unwanted marking material is removed by an external
force applied to the
exposed surface of the superimposed layers. The resolution of the print is
determined by the
cleaning unit/how it applies the external force.
4. Direct method: A receptive layer applied over the transparent film. The
colour motif only adheres
to the receptive film. The metallization following the colour motif only
adheres over the colour
motif. After washup, the colour motive printed over the receptive layer will
exist and the rest will
wash away. Polymers discussed in the article (PVC, PET, PC, etc) have the
correct surface property
to receive metal during metallization. Therefore, any area that is uncoated
with the receptive
layer somehow needs to be masked to prevent metallization. Otherwise to
achieve this, the colour
motif must be flood coated. The flood coat would add cost to the process due
to ink usage, clean
up and disposal.
Accordingly, a security device and method of making such security device is
needed, where the security
device comprises a selectively reflective or metallized surface on a first
side of a transparent film and an
opaque surface on the second side. In particular, the security device would be
simple and relatively low
cost to make, and would result in excellent registration between the images
and/or patterns on the two
sides of the security device.
SUMMARY
Provided herein is a security device for a printed product, the security
device comprising a selectively
reflective or metallized surface on a first side of a transparent or semi-
transparent polymer film and an
opaque surface on the second side. In order to render the security feature or
device more difficult to
copy or counterfeit, metallization, including selective or patterned
metallization, is applied to a printed
image on a transparent/semi-transparent substrate, such that the image is
visible from the second side
of the substrate and is in registration with the patterned metallization.
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Also provided herein is a method for making a security device for a printed
product or security
document. The method comprises the steps of:
a) applying a water-soluble coating over a first portion of a first side of
a transparent/semi-
transparent polymer (PVC, PC, PET, PETG, Nylon, etc);
b) applying a print image on a second portion the first side, wherein the
first portion partially
overlaps the second portion;
c) metallizing the first side by way of physical vapor deposition; and
d) washing the first side to remove the water-soluble coating from the
polymer.
In step a, the first portion may be a negative image of the print image in
step b.
In step b, the inks used to print the image may be inks with high surface
energy after curing.
In step d, washing will also remove anything (e.g. metal, print image, etc
that has been applied over the
water-soluble coat).
The water-soluble coating may be applied by any suitable technique including
but not limited to
flexographic, inkjet, laser, gravure and silk-screening.
Unlike other methods described in the art (see Hoffmuller above), the water-
soluble coating is applied
first, prior to applying the print image, which may be in colour. The print
image and metallization are
done thereafter. Furthermore, the print image is printed so as to overlap the
water-soluble print which
prevents from the printer from dictating the quality of the registration.
After the wash-up step, the print
image and metallization found over the water-soluble coating will wash away.
This would allow for a
tighter registration of the visible print to metallization than Hoffm(iller's
invention.
The method provided herein results in a >1200dpi high resolution image.
In contrast to Hill (discussed above), the whole system is exposed to external
force and only where the
water-soluble coat exists, are the print image and metallization removed ¨
other areas without the
water-soluble coat are unaffected. This allows for a high-resolution image.
DETAILED DESCRIPTION
STEP 1: To obtain a perfectly registered metalized film to a visible image on
a polymer surface, a negative
image is printed with water-soluble coating on a transparent or semi-
transparent film/layer. The film may
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be a thermoplastic polymer and may be made of any suitable substance
including, but not limited to PVC
(polyvinyl chloride), PC (polycarbonate), PET (polyethylene terephthalate),
PETG (polyethylene
terephthalate glycol) and Nylon. A sample image is shown below in Figure 1.
Figure 1. Water soluble coat (white) applied on a
transparent/semi-transparent film is shown.
I IIL, Asa
III bill I
m=== UM= 11111111
Step 2: For the second step, an image, preferably a colour image, will be
printed. The ink used to print the
image will not be soluble in water. To allow metal to bind to the surface of
the image, the inks used for
this process would have a surface energy after curing of >25dynes/cm. Lower
surface energy ink will
deflect the metal from binding to the surface ¨ this may be desirable in some
embodiments . To obtain a
tighter registration with metal to visible print, the visible print must
overlap the water-soluble ink.
I lel 1.1 lea 1411 114 Figure 2. First visible colour (in this example, red)
applied over the
Iel lei 144 lei I film is shown. The registration of the visible colors to the
water-
! Lill KAI 14 I NI = =
soluble coating is not important as the visible colour shall be
printed so as to overlap the water-soluble coat (i.e. in this example,
111 MI all 11111 us the flags are slightly larger than the blank
spaces created by step
mom moo mom mom Nor
1). The overlap would wash away during washup cycle and provide
a perfect registration between visible print to metal.
Figure 3. The second color (in this example, white) applied over the
flag is shown. The flag will be visible on the opposite side though
the transparent/semi-transparent film. The red part of the flag
printed beneath the white will be slightly visible through the white
due to lower opacity of that coating.
STEP 3: In step 3, after the visible prints are completed the metallization
will be applied. Water-soluble
coat, ink and uncoated area will get metallized.
= ..
Figure 4. The metallization is applied over the printed side of the
film is shown.
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The water-soluble coat and inks used for visible print have higher surface
energy, thus allows for
metallization to adhere. Using visible ink with lower surface energy after
curing, such as UV curable hard
coat, would prevent metal from adhering and will form a following artifact.
Figure 5. Metallization over the printed sheet is shown. The ink
with lower surface energy after curing would repel metallization
and produce an unmetallized area.
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STEP 4: After metallization (figure 4) the film goes for wash-up where the
water-soluble coat (applied in
first step) and everything on top of it will get washed away. The result will
be as shown below in Figure 6.
!lel lel lel lel IP 1 AM lilt Figure 6. Face and back
side of the printed and
4,11 14,1IIIII it 11111 metallized film are
shown.
* , 4p 4 ___ , The water-soluble coat is
* *
ai washed away where the
a a a a film is transparent.
The method described herein constitutes an improvement over the previously
described method
developed by Vast Films Ltd. The improvement consists of adding one or more
steps of printing a visible
image in order to obtain a security feature that will produce a visible print
in registration with metallization
at high resolution.
Vast Film's selective/pattern metallization CBN's Security
Feature
Transparent Polymer
Transparent Polymer
Flexographic Print
Flexographic Print (Water Soluble Coat)
(Water Soluble Coat)
Flexographic Print
Metallization
(Visible/invisible Print)
Wash-up Metallization
(Metal removal)
Wash-up
6 (Metal removal)
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As shown in the above flow diagram, to obtain visible print in registration to
metallization, at least one
additional step would be necessary ¨ the addition of a visible print/image.
The designer's creativity can
make the process more complex and the security device more difficult to
counterfeit. The following
elements, including two or more elements in combination, may be included to
create a suitable security
device using the methods described herein.
A. Transparent region
B. Metallized region
C. Visible print
D. Invisible fluorescent print
E. Visible/invisible print in registration over the metallization
a. Metal receptive ink (high surface energy ink)
F. Visible/invisible print in registration around metallization
a. Metal non-receptive ink (low surface energy ink)
To metallize a surface, the surface should have a surface free energy of >25
dyes/cm. If the surface energy
is lower, the metal will be deflected away from the surface. Using this
characteristic, the ink can be chosen
to allow and disallow metallization (compare Figs. 4 and 5, for example).
Typically, the energy curable inks are known to produce hard/cured surface
which makes the surface
energy of the cured ink to lower than 25dyes/cm. This would prevent
metallization. Conventional inks
would accept metallization as the surface energy of the cured ink is typically
higher.
The design of the security device with a large surface of metallization would
allow for personalization of
the security document. The metal applied over the film will be <11.tm in
thickness, preferably ¨ 500
angstroms. Using YAG (yttrium aluminum garnet) or YV04 (yttrium orthovanadate)
laser, the metal can
be ablated. This can be achieved, for example, in an embedded form in an ID
card (in the window) or at
the surface of a passport hinge (typically transparent/semi-transparent
nylon).
The embodiments of the invention disclosed herein are exemplary only, and
various changes and
modifications can be made without departing from the spirit and scope of the
invention. The scope of
the invention is indicated in the appended claims, and all changes that come
within the meaning and
range of equivalents are intended to be embraced therein.
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