U.S. patent application number 12/530639 was filed with the patent office on 2010-02-18 for security device with multiple authentication features.
Invention is credited to Cees Bastiaansen, Thijs Meijer, Robert Jan Vrancken.
Application Number | 20100038598 12/530639 |
Document ID | / |
Family ID | 39434385 |
Filed Date | 2010-02-18 |
United States Patent
Application |
20100038598 |
Kind Code |
A1 |
Bastiaansen; Cees ; et
al. |
February 18, 2010 |
SECURITY DEVICE WITH MULTIPLE AUTHENTICATION FEATURES
Abstract
A security device comprising the following components: a) 30-80
wt % mono-functional LCP's, b) 0-50 wt % higher functional LCP's,
preferably below 50 wt % c) 0-30 wt % liquid crystalline inert
monomers, preferably below 20 wt % d) 0-50 wt % non-liquid
crystalline (mono- or higher) functionalized monomers, preferably
below 30 wt % e) 0-30 wt % non-liquid crystalline inert monomers,
preferably below 20 wt % f) 0.01-10 wt % initiators, preferably
below 2 wt % g) 0.-10 wt % inhibitors, preferably below 2 wt % h)
0.01-50 wt % additives, preferably below 20%, more preferably below
10 wt %, with the provisions that the total amount of the
components is 100 wt %, characterized in that the additives h)
comprise magnetic additives, such as paramagnetic,
super-paramagnetic, diamagnetic or ferri-magnetic particles
Inventors: |
Bastiaansen; Cees;
(Montfort, NL) ; Meijer; Thijs; (Eindhoven,
NL) ; Vrancken; Robert Jan; (Eindhoven, NL) |
Correspondence
Address: |
HAMMER & ASSOCIATES, P.C.
3125 SPRINGBANK LANE, SUITE G
CHARLOTTE
NC
28226
US
|
Family ID: |
39434385 |
Appl. No.: |
12/530639 |
Filed: |
March 11, 2008 |
PCT Filed: |
March 11, 2008 |
PCT NO: |
PCT/EP08/01924 |
371 Date: |
September 10, 2009 |
Current U.S.
Class: |
252/500 ;
252/299.5 |
Current CPC
Class: |
Y10T 428/24802 20150115;
C09K 19/2007 20130101; C09K 19/42 20130101; Y10T 428/10 20150115;
C09D 11/101 20130101; Y10T 428/1005 20150115; C09D 11/34 20130101;
C09K 2019/0448 20130101; C09K 2323/02 20200801; C09K 19/54
20130101; C09K 2323/00 20200801 |
Class at
Publication: |
252/500 ;
252/299.5 |
International
Class: |
C09K 19/54 20060101
C09K019/54; H01B 1/12 20060101 H01B001/12 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 13, 2007 |
EP |
07005119.8 |
Mar 13, 2007 |
EP |
07005120.6 |
Mar 13, 2007 |
EP |
07005122.2 |
Mar 13, 2007 |
EP |
07005123.0 |
Claims
1. A security device comprising the following components: (a) 30-80
wt % mono-functional LCP's (b) 0-50 wt % higher functional LCP's,
preferably below 50 wt % (c) 0-30 wt % liquid crystalline inert
monomers, preferably below 20 wt % (d) 0-50 wt % non-liquid
crystalline (mono- or higher) functionalized monomers, preferably
below 30 wt % (e) 0-30 wt % non-liquid crystalline inert monomers,
preferably below 20 wt % (f) 0.01-10 wt % initiators, preferably
below 2 wt % (g) 0-10 wt % inhibitors, preferably below 2 wt % (h)
0.01-50 wt % additives, preferably below 20%, more preferably below
10 wt %, with the provisions that the total amount of the
components is 100 wt %, characterized in that the additives h)
comprise magnetic additives, such as paramagnetic,
super-paramagnetic, diamagnetic or ferri-magnetic particles.
2. The security device according claim 1 characterized in that the
additives h) comprise additionally or only conductive or
semi-conductive additives.
3. The security device according to claim 2, characterized in that
the conductive or semi-conductive additives are selected from a
group comprising nanometer or micrometer sized rods, flakes,
spheres or otherwise suitably shaped conductive particles of
metals, alloys or semiconductor-based materials.
4. The security device according to claim 3 characterized in that
the conductive or semi-conductive additives are selected from a
group comprising semi-conductive conjugated polymers, such as
polyphenylene vinylene semi-conductive liquid crystals, such as
oligothiophenes, which are preferably LCP's.
5. The security device according to claim 1 characterized in that
the additives h) comprise additionally or only photochromic
pigments or dyes, thermochromic pigments or dyes, electrochromic
pigments or dyes, ionochromic pigments or dyes, halochromic
pigments or dyes, solvatochromic pigments or dyes, trobochromic
pigments or dyes and piezochromic pigments or dyes.
6. The security device according to claim 1, characterized in that
the components are applied to a substrate by means of printing,
such as but not limited to inkjet printing, flexography, offset
printing, screen printing, micro-contact printing, micro-transfer
printing, gravure printing, rotogravure printing, reel-to-reel
printing.
7. The security device according to claim 1, characterized in that
the components are aligned by a substrate layer comprising linearly
photo-polymerizable polymers.
8. The security device according to claim 1, characterized in that
the component are aligned by multiple types of alignment through
the combination of multiple aligning substrates.
9. The security device according to claim 1, characterized in that
the substrates contain further authentication features, such as
holograms, retro-reflecting layers, interference stack reflectors,
fluorescent layers, color-shifting layers or features printed by
means of flakes.
10. The security device according to claim 1, characterized in that
the components from e) through f) are selected such that they do
not prohibit the alignment of the liquid crystals from components
a) through d).
11. The security device according to claim 1, characterized in that
the components from a), b) and d) are functionalized to form a
polymer structure, preferably due to possessing compatible types of
functional groups, very preferable by possessing the same type of
functional group.
12. The security device according to claim 1, characterized in that
the components a) through h) are selected such that
phase-separation is suppressed at least only before polymerization
but preferably also during polymerization.
13. The security device according to claim 1, characterized in that
the device contains information such as e.g. text, numbers, a
barcode, or an image.
14. The security device according to claim 1, characterized that
the additives are in a pattern so that they contain additional,
optionally hidden, information such as e.g., text, numbers, a
barcode or an image.
Description
[0001] The present invention pertains to a security device in
particular as authentication feature for prevention of
counterfeiting of documents and/or products.
[0002] In order to prevent counterfeiting, there is a continuing
need to secure valuable documents and/or products. Adding
authentication features, which are very difficult to forge but
preferably easy to inspect, to these products helps against
counterfeiting. There are many authentication features known in the
art. Many are based on well-known and thus non-distinct optical
effects. Examples of optical authentication features are holograms,
based on diffracting structures, watermarks, based on thickness
differences in semi-opaque substrates and fluorescent markings.
Furthermore, gaining access to the materials and technology to
produce these or highly similar effects is often straightforward.
The strength of authentication features produced with Polymerizable
Liquid Crystals (LCP's) are the many possible optical effects,
which are much less known and very difficult to imitate
[0003] Polymerizable Liquid Crystals (LCP's) are a class of
materials which exhibit one or more liquid crystalline phases, such
as a nematic, smectic or chiral nematic (also called cholesteric)
phase, within a certain temperature range. Furthermore, LCP's can
be polymerized due to reactive groups which are part of the
molecule. Before polymerization, LCP's are monomers, but also after
polymerization the resulting polymers are commonly referred to as
LCP's. In the text, where LCP's are mentioned the monomer form is
referred to; the polymer form is referred to as LCP polymer.
Moreover, the skilled person is able to differentiate between the
polymeric and monomeric LCP's in the context of the specification
and by using his common knowledge. Polymerization of LCP's can be
induced spontaneously at elevated temperatures or aided by means of
suitable initiators, such as for instance photo-initiators or
thermal initiators. Common examples of reactive groups are
acrylates, methacrylates, epoxies, oxethanes, vinyl-ethers,
styrenes and thiol-enes. Here, monomers which by means of reactive
end groups have the ability to form links with two other molecules
are called mono-functional, since two links are the minimum number
required to form a polymer. Monomers with the ability to form links
with more than two other molecules are called higher
functional.
[0004] It is possible to obtain security devices by printing flakes
of LCP polymers which are formulated into an ink, but these flakes
are expensive and difficult to produce as well as apply. Such
flakes are for instance disclosed in EP0968255. The production
process of flakes consists of a number of time-consuming steps
before the flakes are polymerized and broken into pieces of
suitable size. Afterwards, these flakes are mixed into a
transparent polymerizable binder. Due to the average size of the
flakes in the binder as well as the variability of the flake
geometry, the print resolution is limited. Furthermore, flakes are
not suited for inkjet printing as the flakes clog the conduits and
nozzles in the inkjet head. Furthermore, the optical effects are
not as uniform nor as clear and striking as a single layer of
LCP.
[0005] Another method to create security devices containing
LCP-based authentication features is by inkjet printing of LCP's to
form features with distinct optical properties. Furthermore, inkjet
printing allows that each print is made unique, which is especially
useful for instance when a need exists to track and trace each
individual document or product or to include specific information
such as biometric information. The possibility of combining
LCP-based optical effects and inkjet printing is only mentioned in
very few documents, which are all non-specific with regards to the
actual requirements.
[0006] Creating security devices by printing LCP's with solvents
has been described e.g. in EP1381520. Solvents are materials which
cause the LCP's to dissolve in them and together form a solution.
Furthermore, such solvents are usually meant to evaporate after
processing but before polymerization, so the solvent is not
contained in any significant amount in the final product. Examples
of commonly employed solvents for LCP's are xylene, toluene and
acetone. The problem with ink jetting of LCP's is that commercial
inkjet printing equipment is unable to reproducibly print LCP's if
these are dissolved in solvents. Ink jetting solvent based mixtures
leads to a drying effect which is detrimental to the homogeneity of
the prints, the so-called coffee stain effect. Furthermore the use
of solvents can affect the substrates on which the LCP's are
printed and also it can dissolve any previously printed LCP
structure on the substrate before polymerization. When printing
structures containing different materials stemming from different
reservoirs, the use of solvent based mixtures gives rise to
significant mixing of the materials on the substrate, leading to
effects such as `colour bleeding` or highly blurred images.
[0007] Solvents can also chemically attack parts of the print head
or heads and conduits in the printing system, in particular
polymer-based parts. These solvents also often evaporate at or near
the nozzle, leading to clogging. Furthermore, such solvents are
often harmful to the equipment because of corrugation as well as to
people and to the environment due to toxicity and therefore require
extensive equipment for air filtration near the printing equipment.
Furthermore, heating of the printed materials to enhance
evaporation and thus production speed is highly desirable,
requiring heating installations within the production equipment
which increase complexity and cost and also can be detrimental to
the surrounding equipment as well as the substrates on which is
printed.
[0008] Creating of security devices by printing of LCP's without
solvents is also known, e.g. from EP1491332. However, this document
does not describe or teach specific materials or steps to enable
the inkjet printing of LCP's or potential problems related to it.
In particular, mixtures containing LCP's but without solvents are
hardly manageable with the currently available production-ready
equipment. Only with highly dedicated inkjet printing equipment is
it possible to print LCP's, and only at or above 140C, limiting the
scope of security devices to be produced At such temperatures
however, LCP's start to polymerize spontaneously through thermal
excitation of the reactive groups or the initiators in the
mixture.
[0009] To be able to print a mixture with inkjet printing it is
needed that the mixture which is printed is at least chemically
stable for the time it remains in the inkjet head or reservoir at
the temperature at which the mixture is printed, which is in the
order of minutes to weeks depending on the printing speed an the
printer usage.
[0010] It is the object of the present invention to overcome the
limitations of the prior art by providing a security device, which
can be reproducibly printed with state-of-the art equipment, with
the inclusion of various additives.
[0011] It is one object of the invention to provide a security
device that can easily and reproducibly be made by common printing
technologies and at the same time does not show the restriction of
the security devices in the prior art.
[0012] It is another object of the inventions is to show provide
for new LCP based security features by adding one or more of a
range of specific additives to the LCP materials. These materials
can add other authenticating effects to the resulting
authentication feature, thus creating a new authenticating
feature.
[0013] It is another object of the invention to provide a security
device that can be manufactured via printing techniques, which
allows for the creation of arbitrary structures which can contain
information in the form of e.g. barcodes, images, text, numerical
codes.
[0014] Surprisingly, it has been found that the object of the
present invention can be achieved with a security device comprising
the following components: [0015] a) 30-80 wt % mono-functional
LCP's [0016] b) 0-50 wt % higher-functional LCP's [0017] c) 0-30 wt
% liquid crystalline inert monomers, preferably below 20 wt %
[0018] d) 0-50 wt % non-liquid crystalline (mono- or higher)
functionalized monomers, preferably below 30 wt % [0019] e) 0-30 wt
% non-liquid crystalline inert monomers, preferably below 20 wt %
[0020] f) 0.01-10 wt % initiators, preferably below 2 wt % [0021]
g) 0-10 wt % inhibitors, preferably below 2 wt % [0022] h) 0.01-50
wt % additives, preferably below 20%, more preferably below 10 wt
%, with the provisions that the total amount of the components is
100 wt %, wherein the additives h) comprise magnetic additives,
such as paramagnetic, super-paramagnetic, diamagnetic or
ferri-magnetic particles.
[0023] In the following, some non-limitative examples are given of
suitable components.
[0024] An example of category a) is
##STR00001##
where x is between 1 and 10.
[0025] Suitable examples from category d are
##STR00002##
and also
##STR00003##
as well as
##STR00004##
[0026] Acrylates have specific advantages in that they have fast
curing times as well as a wide choice in suitable initiators.
However LCP's with different reactive groups are also known from
literature, and could also be applied with the same method. Epoxies
for instance have the specific advantages that they provide for
good adhesion to many printed surfaces, exhibit relatively small
amounts of polymerization shrinkage and are less affected by oxygen
inhibition during polymerization. Oxethanes have properties
comparable to epoxies, but typically exhibit less polymerization
shrinkage. Thiol-ene based polymerization (including both thiol and
-ene groups in the molecule structure) is also possible.
Vinyl-ethers are also not very sensitive to oxygen inhibition and
polymerize very rapidly, but only at relatively high
temperatures.
[0027] A suitable example of category e) is ethylene glycol.
[0028] Suitable examples of category f) are for instance sold by
Ciba-Geigy (Switzerland), under the trade names Irgacure and
Darocure, and in general polymerization initiators are known in the
art.
[0029] It is further preferred if components or a mixture are
applied to a substrate by means of printing, such as but not
limited to inkjet printing, flexography, offset printing, screen
printing, micro-contact printing, micro-transfer printing, gravure
printing, rotogravure printing, reel-to-reel printing.
[0030] Examples of magnetic additives are paramagnetic,
super-paramagnetic, diamagnetic or ferri-magnetic particles. Such
particles are typically 5 to 500 nm in size. The magnetic
properties can be probed by e.g. magnetoresistive sensors. The
addition of such particles enables the creation of structures that
can be moved mechanically by means of magnetic fields. Such
movement can give rise to e.g. altered optical, mechanical,
electrical or magnetic properties of the printed structure, which
can be used to authenticate the feature.
[0031] It is particularly beneficial that the printed structures
are (in part) made from LCP's, since the anisotropic properties of
the aligned LCP polymer matrix can enhance the magnetic and
mechanical properties desired to fully exploit the magnetic
properties of the print. Especially if the magnetic material is
magnetically anisotropic and also aligning with regards to the LCP
polymer matrix. The anisotropic magnetic properties will then be
macroscopically available.
[0032] A preferred embodiment comprising a magnetuc additive is
shown by the following components: [0033] a) 54.5 wt %
mono-functional LCP acrylate
[0033] ##STR00005## [0034] b) 22 wt % di-functional LCP
acrylate
[0034] ##STR00006## [0035] c) 19 wt % non-reactive LC monomer
K15
[0035] ##STR00007## [0036] f) 1.0 wt % photo-initiator
[0036] ##STR00008## [0037] g) 0.5 wt % inhibitor hydroquinone
[0037] ##STR00009## [0038] h) 3 wt % of magnetic microspheres beads
of mean diameter 0.9 .mu.m diameter containing between 20 and 60%
magnetite in a polystyrene/divinylbenzene matrix
[0039] Components a through h are added in a glass vial and diluted
with paraxylene with a ratio of 1 (mixture):1.25 (paraxylene), and
the resulting mixture is manually stirred for 5 minutes at
70.degree. C. The resulting mixture is then fluid. This mixture is
printed in a 10 .mu.m film with the doctor blading technique on a
tri-acetylcellulose film, which is rubbed with a velvet cloth to
induce alignment. The solvent film is allowed to evaporate at
50.degree. C. during 2 minutes and the resulting film is then
UV-cured in a nitrogen atmosphere.
[0040] The resulting feature is birefringent and contains magnetic
particles which are evenly dispersed in the polymer matrix.
[0041] It is further preferred that the additives h) comprise
additionally or only conductive or semi-conductive additives, more
preferably, conductive or semi-conductive additives that are
selected from a group comprising nanometer or micrometer sized
rods, flakes, spheres or otherwise suitably shaped conductive
particles of metals, alloys or semiconductor-based materials, and
even more preferably conductive or semi-conductive additives are
selected from a group comprising semi-conductive conjugated
polymers, such as polyphenylene vinylene or mixtures of polymers
such as PEDOT-PSS (a mixture of Poly(3,4-ethylenedioxythiophene)
and sodium poly(styrenesulfonate)), and semi-conductive liquid
crystals, such as oligothiophenes, which are preferably LCP's.
[0042] A particular benefit of adding (semi-) conductive or
magnetic additives to the prints is that the authentication is
straightforward by means of electric and magnetic fields or
currents, and the effects can be reversible enabling
non-destructive authentication. Furthermore, a particular benefit
of inkjet printing such structures is that these additives can be
printed in varying structures, thus enabling unique and
identifiable responses to electrical or magnetic fields.
[0043] Conductive additives enable the printing of electronic
circuits. Such circuits can be used for instance to create optical
effects which are switchable by means of electrical signals. The
conducting properties of the structure itself too can be used as an
authentication feature. This can be done particularly effectively
if elements of electronic circuits, such as FET's, diodes or
capacitors are created within the print, since these give rise to
designable and clearly identifiable electronic responses. It is
possible that the conductive structures are used to make switchable
another, adjacent non-conductive printed structure, either of which
is not necessarily but preferably applied by means of inkjet
printing. Such multi-layered prints are advantageously created
sequentially or concurrently, either in a single layer or in
separate layers, printed either on top of or next to each other or
even on opposite sides of the substrates or on multiple substrates
which are assembled together after printing. Furthermore, it is
possible to create structures which are conductive and contain
electroluminescent or electrochromic additives, which can be
addressed (made to change the optical appearance of the feature) by
currents flowing through the printed structure itself. Furthermore,
by supplying charges of equal or opposite sign to two electrically
isolated by adjacent parts of the structure, capacitors can be
formed. If such parts of the structure are able to move
mechanically, such movement can give rise to e.g. altered optical,
mechanical, electrical or magnetic properties of the printed
structure, which can be used to authenticate the feature.
[0044] It is particularly beneficial that the printed structures
are (in part) made from LCP's, since the anisotropic properties of
the aligned LCP polymer matrix can enhance the electrical and
mechanical properties desired to fully exploit the conductive
properties of the print.
[0045] It is further preferred that the security device according
to the invention comprises additionally or only additives h) in the
form of photochromic pigments or dyes, thermochromic pigments or
dyes, electrochromic pigments or dyes, ionochromic pigments or
dyes, halochromic pigments or dyes, solvatochromic pigments or
dyes, trobochromic pigments or dyes and piezochromic pigments or
dyes, fluorescent of phosphorescent pigments or dyes.
[0046] It is further preferred that these optical additives show
anisotropic optical properties and that they align with the LCP
material in the security device. This gives the entire security
device additional anisotropic optical properties.
[0047] It is preferred for inventive security device if the
components or a mixture of the components are applied to a
substrate by means of printing, such as but not limited to inkjet
printing, flexography, offset printing, screen printing,
micro-contact printing, micro-transfer printing, gravure printing,
rotogravure printing, reel-to-reel printing.
[0048] In addition, it is preferred for the security device that
during the manufacturing process manufacture the components are
aligned by a substrate layer comprising linearly
photo-polymerizable polymers, preferably by aligned multiple types
of alignment through the combination of multiple aligning
substrates.
[0049] Preferably these substrates contain further authentication
features, such as holograms, retro-reflecting layers, interference
stack reflectors, fluorescent layers, color-shifting layers or
features printed by means of flakes.
[0050] It is preferred for the security device if the components
from e) through h) are selected such that they do not prohibit the
alignment of the liquid crystals from components a) through d).
[0051] Preferred security devices contain components from a), b)
and d) that are functionalized to form a polymer structure,
preferably due to possessing compatible types of functional groups,
very preferable by possessing the same type of functional
group.
[0052] Moreover, the inventive security device preferably comprises
components a) through h) that are selected such that
phase-separation is suppressed at least only before polymerization
but preferably also during polymerization.
[0053] By applying such components printing is easily possible
below 120.degree. C., preferably below 100.degree. C., very
preferably 80.degree. C., to achieve security devices with
distinctive and reproducible optical effects. In particular, it is
also possible to add solvents to mixtures of these components which
makes the mixture applicable to various printing techniques.
[0054] Combinations of different initiators can be used which has a
number of potential advantages, of which a number are now
described.
[0055] Different initiators will give different mechanical
properties of the mixture before and after polymerization. Using
mono-functional initiators can allow for a low viscosity of the
mixture. However, multifunctional initiators tend to be more
viscous. The exact choice of initiators also influences e.g. the
flexibility and toughness of the polymerized structure.
Furthermore, the choice of photo-initiator is dependent on the
presence of other absorptive additives in the mixture, which will
be described below at category h). It is possible to use mixtures
of initiators which in these cases too allow for a good
polymerization of both the top layer of the structure as well as
throughout the structure. An initiator that can overcome oxygen
inhibition of the surface can be used to initiate polymerization at
the surface, whereas another initiators can be used to through-cure
the structure. It is also possible to choose initiators in such a
way that only the top of the structure polymerizes, but the
remaining part remains non-polymerized. The non-polymerized LCP is
then still fluid, and can be manipulated by means of for instance
electric or magnetic fields, i.e. they remain switchable.
[0056] The list of other possible additives from category h)
contains, but is not limited to, the following examples.
[0057] One example of additives are molecules that can act as
tracer molecules, such as e.g. DNA-molecules. These can be added in
minute quantities, typically with amounts in the order of one part
per million (ppm), so that they are very difficult to trace when
their exact properties are not known beforehand.
[0058] Another example of additives are surfactants, which can
enhance alignment of the liquid. These surfactants can either
enhance the alignment of the liquid crystalline matrix at the top
of the structure, at the bottom or in the bulk or in combinations
of those locations. Furthermore, these surfactants can influence
the potential phase separation of the mixture or influence the
mechanical properties (e.g. viscosity, surface tension) of the
mixture on the substrate or can perform a combination of these
three functions.
[0059] Another example of additives are chiral additives, commonly
referred to as chiral dopants, which are used to induce a chiral
phase in the liquid crystal structures. Such chiral structures
reflect light from a specific tunable wavelength range and with a
specific handedness, which can either be commonly called left- or
right-handed, and the handedness is determined by the handedness of
the chirality of the structure. It is noted that one or more of the
LCP's from categories a) through c) can also exhibit intrinsic
chiral phases, and/or induce such a phase for all the liquid
crystal molecules. By making use of chiral LCP's, a chiral
structure can be obtained without the use of chiral additives. Many
chiral additives are known to the person skilled in the art.
Preferably the chiral additives are also polymerizable, which has
the advantage that the temperature dependence of the reflected
wavelength is usually decreased.
[0060] Other examples of additives are pigments and dyes. Pigments
and dyes can be added to give the mixture an intrinsic color by
means of absorption of part of the spectrum as well as luminescence
in part of the spectrum. Such intrinsic color can enhance the
optical effects of the printed structure, for instance by enhancing
contrast of (parts of) the printed structure.
[0061] Pigments are particles which do not dissolve molecularly in
the mixture whereas dyes can be approximately molecularly
dissolved. The choice between pigments and dyes is dependent on
various factors. One important factor is the solubility of the dyes
or the pigments, with or without the aid of a dispersant, to create
a stable ink. Solutions with dyes are generally easier to process
than dispersions with pigment, but the optical properties of
pigments are usually more stable. Furthermore, certain optical
additives are only available as pigments and not as dyes, such as
di-electric stacks, whose optical effects are not based on
molecular effects, but on effects on a larger scale. Another
important factor is the price of pigments, which is usually higher
than that of dyes.
[0062] Examples of absorbing pigments or dyes are for instance
[0063] Absorbing only, meaning that a specific part of the spectrum
is absorbed [0064] Photochromic pigments or dyes, which by
excitation with light of a particular part of the spectrum
reversibly change into another chemical species having a different
absorption spectrum from the original chemical species.
Non-reversible photochromic pigments and dyes also exist for
specific purposes [0065] Thermochromic pigments or dyes, which
exhibit a reversible change in absorption spectrum through the
application of heat (i.e. at raised or lowered temperatures).
Non-reversible thermochromic pigments and dyes also exist for
specific purposes [0066] Electrochromic pigments or dyes, which
exhibit a change in absorption spectrum through the addition of
electron charges [0067] Ionochromic pigments or dyes, which exhibit
a change in absorption spectrum through the addition of ionic
charges. [0068] Halochromic pigments or dyes, which exhibit a
change in absorption spectrum through changes in pH. [0069]
Solvatochromic pigments or dyes which exhibit a change in
absorption spectrum through changes in the polarity of the solvent
which is in contact with them. [0070] Tribochromic pigments or
dyes, which exhibit a change in absorption spectrum as a result of
friction applied to them. [0071] Piezochromic pigments or dyes,
which exhibit a change in absorption spectrum through changes in
the pressure applied to them.
[0072] Examples of luminescent pigments or dyes are for instance
[0073] Fluorescent pigments or dyes, which exhibit absorption of
light in a particular part of the spectrum and emission in another
part of the spectrum, typically at a lower wavelength, where the
absorption and emission of individual photons occur subsequently
but with delays of typically nano-seconds. [0074] Phosphorescent
pigments or dyes exhibit similar absorption and emission as
fluorescent dyes, but due to a different quantum mechanical decay
mechanism typically emit photons after absorption with much larger
delays of up to hours or days. [0075] Chemoluminescent pigments or
dyes, which exhibit emission of photons as a result of chemical
reactions of the pigments and dyes. Such reactions are generally
non-reversible. [0076] Electroluminescent pigments or dyes, which
exhibit emission of photons as a result of radiative recombinations
of electrons and holes within the pigments or dyes. Such radiative
recombination can occur if an electric current is passed through
the pigments or dyes, or alternatively of they are subjected to
strong electric field capable of exciting electron-hole pairs which
subsequently recombine. [0077] Triboluminescent pigments or dyes,
which exhibit emission of photons as a result of friction applied
to them. [0078] Piezoluminescent pigments or dyes, which exhibit
emission of photons as a result of pressure applied to them. [0079]
Radioluminescent pigments or dyes, which exhibit emission of
photons as a result of ionizing radiation, such as beta particles,
applied to them.
[0080] There are also pigments or dyes which combine multiple
optical effects within a single additive, or which in fact an
effect which is related to multiple causes concurrently. Examples
are [0081] Thermochromic pigment capsules which change colour if
heated above a certain threshold temperature. At this temperature
the crystalline solvent in the capsule melts and effectively lowers
the pH. This in turn causes the halochromic compound present to
change its absorptive properties.
[0082] Photochromic fluorescent dyes are dyes which exhibit
fluorescence only after the molecule has absorbed photons from a
part of the spectrum which it does not absorb in its subsequent
fluorescent state. This effect which is concurrently photochromic
and fluorescent, i.e. due to the first absorption not only the
absorptive properties of the molecule changes (photochromism) but
also the molecule subsequently exhibits fluorescence or a change in
its fluorescent properties
[0083] A preferred embodiment comprising a phosphorescent additive
is shown by the following components:
a) 53.5 wt % mono-functional LCP acrylate
##STR00010##
b) 21.5 wt % di-functional LCP acrylate
##STR00011##
c) 18.5 wt % non-reactive LC monomer K15
##STR00012##
f) 1.0 wt % photo-initiator
##STR00013##
g) 0.5 wt % inhibitor hydroquinone
##STR00014##
h) 5 wt % of phosphorescent pigment PPSB-03, from RiskReactor,
California, USA,
[0084] Components a through h are added in a glass vial and diluted
with paraxylene with a ratio of 1 (mixture):1.25 (paraxylene), and
the resulting mixture is magnetically stirred for 5 minutes at
70.degree. C. The resulting mixture is then fluid. This mixture is
printed in a 40 .mu.m film with the doctor Blade technique on a
tri-acetylcellulose film, which is rubbed with a velvet cloth to
induce alignment. The solvent film is allowed to evaporate at
50.degree. C. during 2 minutes and the resulting film is then
UV-cured in a nitrogen atmosphere.
[0085] The resulting feature is birefringent and contains
phosphorescent particles which are evenly dispersed in the polymer
matrix.
[0086] When the resulting feature is viewed between crossed
polarizers, the birefringence is clearly visible. When the
alignment axis of the feature is parallel to either polarizer, the
feature is dark between the polarizers. When the alignment axis of
the feature is at 45 degrees to both polarizers, the feature is
bright between the crossed polarizers. When the feature is placed
under a UV light, the phosphorescent particles lights up bright
orange. When the UV light is turned off, the bright orange glow
remains for about half a minute.
[0087] A preferred embodiment comprising a photochromic additive is
shown by the following components:
a) 53.5 wt % mono-functional LCP acrylate
##STR00015##
b) 21.5 wt % di-functional LCP acrylate
##STR00016##
c) 18.5 wt % non-reactive LC monomer K15
##STR00017##
f) 1.0 wt % photo-initiator
##STR00018##
g) 0.5 wt % inhibitor hydroquinone
##STR00019##
h) 5 wt % of photochromic blue pigment (IT9 014) from MUTR, Herts,
UK
[0088] Components a through g are added in a glass vial and diluted
with paraxylene with a ratio of 1 (mixture):1.25 (paraxylene), and
the resulting mixture is magnetically stirred for 5 minutes at
70.degree. C. The resulting mixture is then fluid. Component h is
then added, dissolved in ethanol with a ratio of 1 (component h):10
(ethanol). The mixture is then vigorously stirred magnetically for
30 seconds. This mixture is printed in a 40 .mu.m film with the
doctor Blade technique on a tri-acetyl cellulose film, which is
rubbed with a velvet cloth to induce alignment. The solvent film is
allowed to evaporate at 50.degree. C. during 2 minutes and the
resulting film is then UV-cured in a nitrogen atmosphere.
[0089] The resulting feature has the pigment dispersed throughout
the polymer matrix. The resulting feature is birefringent, but due
to the dispersed pigment it is also scattering. The birefringence
is visually inspected between crossed polarizers. When the
alignment axis of the feature is parallel to either polarizer, the
feature is dark but the scattering due to the pigments gives rise
to some transmission of light. When the alignment axis of the
feature is at 45 degrees to both polarizers, the feature is bright
between the crossed polarizers. The resulting feature has a yellow
colour, when the resulting feature is placed in a UV-light for 30
seconds, the colour turns to blue. When the feature is no longer in
the UV-light it retains the blue colour for a few minutes and then
returns to yellow again.
[0090] A preferred embodiment comprising a thermochromic additive
is shown by the following components:
[0091] A preferred embodiment are the following components:
a) 53.5 wt % mono-functional LCP acrylate
##STR00020##
b) 21.5 wt % di-functional LCP acrylate
##STR00021##
c) 18.5 wt % non-reactive LC monomer K15
##STR00022##
f) 1.0 wt % photo-initiator
##STR00023##
g) 0.5 wt % inhibitor hydroquinone
##STR00024##
h) 5 wt % of thermochromic pigment IT9 007 "magenta" from MUTR,
Herts, UK
[0092] Components a through g are added in a glass vial and diluted
with paraxylene with a ratio of 1 (mixture):1.25 (paraxylene), and
the resulting mixture is magnetically stirred for 5 minutes at
70.degree. C. The resulting mixture is then fluid. Component h is
then added, dissolved in ethanol with a ratio of 1 (component h):10
(ethanol). The mixture is then vigorously stirred magnetically for
30 seconds. This mixture is printed in a 40 .mu.m film with the
doctor blading technique on a tri-acetylcellulose film, which is
rubbed with a velvet cloth to induce alignment. The solvent film is
allowed to evaporate at 50.degree. C. during 2 minutes and the
resulting film is then UV-cured in a nitrogen atmosphere.
[0093] The resulting feature has the pigment dispersed throughout
the polymer matrix. The resulting feature is birefringent, but due
to the dispersed pigment it is also scattering. The birefringence
is visually inspected between crossed polarizers. When the
alignment axis of the feature is parallel to either polarizer, the
feature is dark but the scattering due to the pigments gives rise
to some transmission of light. When the alignment axis of the
feature is at 45 degrees to both polarizers, the feature is bright
between the crossed polarizers. When the resulting feature is at
room temperature it has a red colour, when the feature is heated to
50.degree. C. the red colour disappears. When the feature is cooled
down to room temperature the red colour re-appears.
[0094] A preferred embodiment comprising a fluorescent additive and
magnetic particles is shown by the following components: [0095] a)
53.3 wt % mono-functional LCP acrylate
[0095] ##STR00025## [0096] b) 21.6 wt % di-functional LCP
acrylate
[0096] ##STR00026## [0097] c) 18.6 wt % non-reactive LC monomer
K15
[0097] ##STR00027## [0098] f) 1.0 wt % photo-initiator
[0098] ##STR00028## [0099] g) 0.5 wt % inhibitor hydroquinone
##STR00029##
[0099] h1) 3 wt % of magnetic microspheres beads of mean diameter
0.9 .mu.m diameter containing between 20 and 60% magnetite in a
polystyrene/divinylbenzene matrix h2) 2% DFSB-K44-65 fluorescent
dye from RiskReactor, California, USA.
[0100] Components a through h2 are added in a glass vial and
diluted with paraxylene with a ratio of 1 (mixture):1.25
(paraxylene), and the resulting mixture is manually stirred for 5
minutes at 70.degree. C. The resulting mixture is then fluid. This
mixture is printed in a 20 .mu.m film with the doctor blading
technique on a tri-acetylcellulose film, which is rubbed with a
velvet cloth to induce alignment. The solvent film is allowed to
evaporate at 50.degree. C. during 2 minutes and the resulting film
is then UV-cured in a nitrogen atmosphere.
[0101] The resulting feature is birefringent and contains magnetic
particles which are evenly dispersed in the polymer matrix. The
birefringence is visually inspected between crossed polarizers.
When the alignment axis of the feature is parallel to either
polarizer, the feature is dark. When the alignment axis of the
feature is at 45 degrees to both polarizers, the feature is bright
between the crossed polarizers. Under a microscope the dispersed
magnetic particles are clearly visible. When placed under a
UV-lightsource it shows bright yellow fluorescence. This
fluorescence is isotropic in emission and absorption.
[0102] Pigments and dyes can exhibit anisotropic optical
properties, depending on their molecular orientation. If
anisotropic dye molecules align to a significant degree within the
LCP matrix, typically parallel or perpendicular to the LCP
alignment, typically caused by a distinct anisotropic molecular
shape, these molecules can exhibit their anisotropic optical
properties collectively, leading to distinctive optical effects,
which remain after polymerization of the LCP matrix. This effect is
commonly known as dichroism or pleochroism. Pigments can also
exhibit dichroic effects if the particles as such have anisotropic
optical properties. However, such properties are difficult to
exploit since for a collective effect all pigments have to be
effectively aligned in the direction of their inherent
anisotropy.
[0103] It is possible to create features which exhibit fluorescent
dichroism in absorption but not in emission or vice versa. This
effect can be achieved for instance by using two fluorescent
molecular species, one of which absorbs and emits essentially
non-dichroic and the other essentially dichroic. By choosing both
species in such a way that the absorbed photon-energy is
transferred to the other species, such effects can be obtained.
Also, fluorescent molecules can exhibit different degrees of
dichroism in absorption and emission, but the effect with using
multiple suitably chosen species is in general more pronounced.
[0104] A preferred embodiment comprising an anisotropic fluorescent
additive is shown by the following components: [0105] a) 54.5 wt %
mono-functional LCP acrylate
[0105] ##STR00030## [0106] b) 22 wt % di-functional LCP
acrylate
[0106] ##STR00031## [0107] c) 19 wt % non-reactive LC monomer
K15
[0107] ##STR00032## [0108] f) 1.0 wt % photo-initiator
[0108] ##STR00033## [0109] g) 0.5 wt % inhibitor hydroquinone
[0109] ##STR00034## [0110] h) 3 wt % of an anisotropic fluorescent
dye DFSB-K82 from RiskReactor, California, USA.
[0111] Components a through h are added in a glass vial and diluted
with paraxylene with a ratio of 1 (mixture):1.25 (paraxylene), and
the resulting mixture is magnetically stirred for 15 minutes at
70.degree. C. The resulting mixture is then fluid and clear. This
mixture is printed with printed in a 10 .mu.m film with a doctor
blading technique on a tri-acetylcellulose film, which is rubbed
with a velvet cloth to induce alignment. The solvent film is
allowed to evaporate at 50.degree. C. during 2 minutes and the
resulting film is then UV-cured in a nitrogen atmosphere. The
resulting film is birefringent. When placed under a UV-lightsource
it shows bright yellow fluorescence. This fluorescence is
anisotropic in emission: when the emission is inspected visually
through a polarizing filter the emission is high for one
polarization direction and low for the orthogonal polarization
direction. The difference between the high and low emission is
optically very distinctive, giving the security feature a striking
effect.
[0112] When using the same mixture described above, only with
different fluorescent dyes, we have also obtained layers that show:
[0113] isotropic fluorescence in both emission and absorption with
dye DFSB-K44-65 from RiskReactor, California, USA, [0114]
anisotropic fluorescence in both emission and absorption with dye
DFSB-K61.
[0115] The anisotropy of the emission is inspected optically by
viewing the emission through a polarizing filter which is rotated,
while the UV-source is not polarized. The anisotropy of the
absorption is inspected optically: a UV-polarizing filter is placed
in front of the UV source and the sample is then rotated, while the
emission is inspected.
[0116] UV-absorbing pigments and dyes or pigments can serve several
specific purposes. Such UV-protecting pigments and dyes can be
present in the printed mixture or applied over the printed
structure after curing by another printing step, preferably by
means of flexography or offset printing. Also other application
methods can be employed, such as bar-coating, doctor blading,
spraying or by applying a UV-absorbing substrate on top of the
printed substrate.
[0117] As these pigments or dyes absorb UV light, they can protect
the printed layer, or the substance underneath this layer, from
harmful UV-radiation which can lead to degradation of the
(mechanical) properties of the structures, such as brittling.
During the UV-curing of the printed layer, UV-absorbers can also be
used to prevent the deeper parts of the layer of being polymerized,
thus allowing for a non-polymerized layer to exist, whereas the top
layer is solidified during polymerization. Also, such a
non-polymerized layer is not created but there is formed a gradient
in the structure if specific components of the mixture diffuse
towards or away from the higher polymerized regions during
polymerization. Such gradients create new optical effects. For
instance, a gradient in the amount of chiral dopant leads to
structures after polymerization which exhibit a gradient in the
chiral pitch, thus reflecting light over a greater wavelength range
than a single pitched structure would. This effect is known as a
broadband cholesteric mirror.
[0118] Again it has to be emphasized that the additives mentioned
above can either be present together or separately in the mixture.
It goes without saying, however, that the total amount of
components forming the polymerizable mixture is always 100 wt
%.
[0119] As the anisotropic optical properties of the LCP's in the
matrix before and after polymerization are dependent on their
alignment, the preferred substrates on which is printed induce or
do not interfere with the alignment of the LCP's so as to obtain
the desired optical effect. Commonly used substrates are rubbed
polyimide, as well as rubbed tri-acetyl-cellulose, polyethylene
terephthalate, polyethylene or polypropylene. Rubbing causes planar
aligning properties for these substrates.
[0120] Other substrates, also substrates causing other types of
homogenous alignment, are known in the art as well. Common types of
alignment are e.g. planar, homeotropic and tilted alignment.
[0121] LPP (Linearly Photopolymerizable Polymers) layers can also
be used as alignment layers. LPP allows for the patterning of the
alignment layer by means of polarized light and thus multi-domain
patterning of the alignment layer. Furthermore it is possible to
use self-assembled mono-layers (SAM's) as alignment layers, which
can easily be applied in a pattern by e.g. printing. Combinations
of for instance SAM's and LPP or tri-acetyl cellulose layers allow
for an increased control over the alignment of the LCP's in the
azimuthal and polar direction.
[0122] Next to the aligning properties of the surfaces, the choice
in substrates also determines the interactions between the mixture
and the substrate. These interactions can be used to create
additional (optical) effects. E.g. the use of hydrophobic of
hydrophilic (chemically) patterned surfaces allows for print
confinement and thus a higher print resolution and more striking
optical effects. A geometrically patterned surface can also be used
to confine printed ink. Confinement can lead to printed structures
with more controlled geometries, leading to better defined
properties which are beneficial for authentication purposes. Such
chemical or geometrical patterning of the substrates can be
achieved by means of printing, but also other techniques such as
for instance embossing, rubbing and lithography.
[0123] The optical properties of the employed substrates influence
the overall properties of the security feature. Such substrates can
be combined, i.e. stacked on top of each other creating a
multi-layered security feature, or a security feature created on a
stack of substrates each having particularly beneficial properties.
Dependent on the preferred optical effects, the substrates can be
transparent, absorbing in any range of wavelengths, scattering or
reflecting or can comprise patterns of these effects. The
substrates can also have other optical properties. Examples are the
ability to transmit only one polarization, as is the case with
polarization films which transmit only one linear polarization, or
the ability to reflect only one polarization, e.g. cholesteric
films only reflect one handedness of light. Furthermore the
substrates can change the polarization of transmitted or reflected
light, as is the case with for instance retarder films and half
wave plates.
[0124] The substrates can also contain other authentication
features. Examples are holograms, retro-reflecting layers,
interference stack reflectors, fluorescent layers, color-shifting
layers or features printed by means of flakes. It is also possible
to add layers containing other authentication features on top of
the LCP polymer structures, via e.g. lamination.
[0125] It is preferred that the as-produced features are created
such that they can be applied as tamper evident labels to products
or documents. Such labels have properties which render the intact
removal of the labels very difficult. Such properties could be poor
mechanical integrity, for instance features which have low
toughness, i.e. low resistance to tearing. Furthermore, the
features upon removal can leave behind clear traces of its previous
presence, for instance by means of rupture-sensitive ink
particles.
[0126] It is also preferred that the features can easily be applied
to the documents and products. Such application can for instance be
by means of hot-embossing or by creating self-adhesive
features.
[0127] Printing of LCP's is a very flexible technique, which allows
for many novel optical designs, for instance by using multiple inks
which allows for the concurrent printing of inks with different
optical properties. Of course it is also possible to print on top
of or underneath layers printed via different printing technique's,
such as flexography, laser printing, offset printing, screen
printing, micro-contact printing, micro-transfer printing, intaglio
printing, gravure printing, rotogravure printing, reel-to-reel
printing, and thermal transfer printing.
[0128] Such printing could be done in series or parallel depending
on the printing equipment design. All these options enable a great
host of embodiments with specific uses for specific purposes. In
the following paragraph a few of the options are mentioned,
although this is not an exhaustive list of the possibilities of
printing LCP's.
[0129] The combination of normal black or colored inks with LCP
inks, can allow for the inclusion of overt features on top of
normal printed information by printing retarding structures on top
of an image or text printed with regular ink on a reflection
substrate. It can also allow for the enhancement or decrease of
contrast by contrast by printing cholesteric LCP mixtures on top of
an image.
[0130] By using inks with identical apparent color but with
different reflective properties, such as left-hand and right-hand
reflecting cholesteric LCP's, hidden information can be printed
which can only be revealed using a polarization sensitive device or
machine reader. The combination of color-shifting non-liquid
crystal inks and color shifting LCP ink creates the identical
effect, as one ink has a uniform reflection and the other is
polarization selective. The combination of inks with various
additives, but with the same optical properties also allows for
hidden information to be printed.
[0131] Printing several layers on top of each other can enhance
reflectivity or enhance the colors printed.
[0132] Self-authenticating structures can be printing by using e.g.
structured polarizers and a LC structure on a reflective surface,
which can be folded together to create additional effects. This can
also recover encrypted data.
[0133] As is already clear from the above descriptions, it is a
particular advantage of inkjet printing of LCP's that it is
possible to create authentication features with (multiple) overt,
covert, forensic and biometric levels of security, which will be
explained below. Also, it is possible to use one of multiple
options or combinations of options in each level by suitably
choosing (combinations of additives such as pigments and dyes,
substrates, printing procedures and designs of the layers present
in the authentication features.
[0134] Features which incorporate levels of security that are
directly apparent (in particular visible) to anyone without the use
of additional devices, like the color-shifting effect, which can be
seen if a printed chiral nematic structure is tilted, are known as
overt. Any overt security feature should be easily recognizable,
but very difficult to counterfeit. Other examples are multi-color
prints of liquid crystal color-shifting inks.
[0135] Covert levels of security can only be made apparent using
simple devices. For instance, the birefringent nature of LCP's can
be revealed using simple devices such as polarizers if choosing
suitable designs. Examples are nematic structures printed on a
reflecting substrate, which shows reflection or no reflection when
viewed through an polarizer at 0 or 45 degrees to the alignment
axis. Another example is a chiral nematic print, which reflects
only one handedness of circularly polarized light. This can be
discerned by a circular polarizer. Parts of the printed structure
which could be left non-polymerized could be electromagnetically
switched if having anisotropic dielectric constants, as is the case
for many inert liquid crystals. This changes the optical properties
of the structures. In use it is sometimes preferred that the covert
level is not visible as a security feature (i.e. being without a
combined overt level), but consists of e.g. (electro-) magnetically
stored information, micro-text invisible to the eye, etc. For both
optical and other covert layers it is usually possible to devise a
procedure and associated device which performs a fully automatic
authentication.
[0136] A more complicated level of security is the forensic level
of security. This level is usually only known in detail by a
selected group of users, who typically have access to expensive
readout equipment. Possibilities for this level are to add tracer
molecules to the printing ink, which can traced using highly
advanced analysis techniques such as NMR scans. Other options are
to analyze the exact ink content, or to investigate a specific size
and shape of printed dots.
[0137] Finally the biometric level of security allows a feature to
store unique information, typically employed for e.g. tracking and
tracing or authenticating persons. Due to the flexibility of the
printing processes of LCP's, it is possible to print e.g. barcodes,
serial numbers, images and other information.
[0138] The availability of additives in the security device can
also be used as an additional biometric level. If the additives are
not evenly dispersed throughout the security device, but in a
predetermined pattern, they can contain more information, which can
be hidden until a proper read-out mechanism is used. This can be
achieved by using different inks to create one device, which are in
composition equal, except for the addition of e.g. magnetic,
conductive or optical additives.
[0139] An example is the local use of magnetic additives in a
barcode printed with nematic LCP inks on a planar aligning
reflecting substrate. The barcode is printed with two LCP inks
which are identical except that one contains magnetic additives,
where the upper half is printed with the ink containing magnetic
additives and the lower half is printed with the ink without the
magnetic additives. The barcode can now be inspected visually using
a polarizer, since the entire barcode is birefringeng. The barcode
will be non visible if the polarizer has its polarization direction
parallel or orthogonal to the alignment direction of the LCP, the
barcode turn dark at a 45 degree angle to the alignment direction
of the LCP. By using a magnetic sensor, such as a magnetoresistive
sensor, the upper half can be inspected magnetically, whereas the
lower half will give no magnetic signal.
* * * * *