U.S. patent application number 10/721104 was filed with the patent office on 2004-06-24 for optical component.
This patent application is currently assigned to Rolic AG. Invention is credited to Moia, Franco.
Application Number | 20040120040 10/721104 |
Document ID | / |
Family ID | 32599066 |
Filed Date | 2004-06-24 |
United States Patent
Application |
20040120040 |
Kind Code |
A1 |
Moia, Franco |
June 24, 2004 |
Optical component
Abstract
An optical component contains two or more hidden images for
authentication and antiforgery purposes. The images are
successively revealed and concealed when the optical component is
held between two polarisers and one of them is rotated. The optical
component comprises one or more optical retarder(s) in which the
images are embedded in separate adjacent stripes or areas, each
image being associated with a different mode of interaction with
polarised light. Instead of two polarisers, one will suffice if the
component is mounted on a reflector.
Inventors: |
Moia, Franco; (Frenkendorf,
CH) |
Correspondence
Address: |
FINNEGAN, HENDERSON, FARABOW, GARRETT & DUNNER
LLP
1300 I STREET, NW
WASHINGTON
DC
20005
US
|
Assignee: |
Rolic AG
|
Family ID: |
32599066 |
Appl. No.: |
10/721104 |
Filed: |
November 26, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10721104 |
Nov 26, 2003 |
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09831524 |
May 10, 2001 |
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09831524 |
May 10, 2001 |
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PCT/IB99/01810 |
Nov 10, 1999 |
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Current U.S.
Class: |
359/489.06 ;
359/489.07; 359/489.15; 359/490.02 |
Current CPC
Class: |
D21H 21/48 20130101;
B42D 25/373 20141001; G02B 5/3083 20130101; Y10S 283/902 20130101;
B42D 25/391 20141001; G07D 7/003 20170501; B42D 25/29 20141001;
B42D 25/00 20141001 |
Class at
Publication: |
359/485 ;
359/483 |
International
Class: |
G02B 005/30 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 13, 1998 |
GB |
98 25 023.6 |
Claims
1. An optical component, comprising one or more retarder(s) in
which is/are embedded a plurality of images, the images being so
arranged that, at any point in the plane of the component, an
element of not more than one image is present, each image being
associated with a different interaction with polarised light.
2. An optical component according to claim 1, wherein there is a
plurality of retarders in which the images are embedded, the
retarders having the same or different retardation values
.DELTA.nd.
3. An optical component, according to claim 1 or 2, wherein the
images are embedded in one or more retarder(s) having specific
image patterns each having a different optical axis from the other
specific image patterns.
4. An optical component according to any preceding claim, wherein
the respective images are contained in alternate areas.
5. An optical component according to any preceding claim, wherein
the respective images are contained in successive optionally
parallel stripes.
6. An optical component according to claim 4 or 5, wherein the
areas or stripes are smaller or narrower than the eye can resolve
enabling an optical component wherein one or more image(s) is/are
(a) photographic image(s).
7. An optical component according to claim 4, 5 or 6, wherein there
are n mages, each respectively being represented on every nth
stripe or nth area.
8. Element for protection against forgery and/or copying,
characterized by an optical component according to any one
preceedingd claims.
9. A viewing system, comprising a source of polarised light, an
optical component according to any preceding claim, through which
component the polarised light can travel, and an analyser for light
which has traversed the optical component, the analyser being
rotatable about the axis of the direction of travel of the light;
whereby, by rotating the analyser, peaks of maximum contrasts for
each image are obtained at specific rotation angles of the
analyser, enabling, at each such angle, visualisation of a
respective image not otherwise visible.
10. A system according to claim 8, wherein the source of polarised
light is a polarising sheet applied to the surface of the
component.
11. A system accorded to claim 9 or 10, wherein the analyser is a
polarising sheet.
12. A viewing system, comprising a reflector which maintains the
polarisation direction of incident light, an optical element
according to claims 1 to 7 attached to said reflector, and a
polariser which is rotatable about the axis of the direction of
travel of the light, such that light which has traversed the
polariser and the optical component is reflected at said reflector
and traverses a second time the optical component and said
polariser; whereby, by rotating said polariser, peaks of maximum
contrasts for each image are obtained at specific rotation angles
of the polariser, enabling, at each such angle, visualisation of a
respective image not otherwise visible.
Description
[0001] The invention relates to an optical component containing a
normally hidden image.
[0002] A particular use of the components according to the
invention is in the field of protection against forgery and copying
and simple yet unambiguous document authentication.
[0003] The increasingly high-quality copying techniques which are
becoming available make it increasingly difficult to safeguard
banknotes, credit cards, securities, identity cards and the like
against forgery. Furthermore, counterfeit branded products (even
including counterfeit pharmaceuticals) and copies of
copyright-protected products, for example compact discs, computer
software and electronics chips, are being produced and distributed
worldwide. The increasing number of forgeries necessitates new
authentication elements which are safeguarded against forgery and
can be identified both visually and by machine.
[0004] In the field of copy-protecting banknotes, credit cards
etc., there are already a considerable number of authentication
elements. Depending on the value of the document to be protected,
very simple or relatively highly complex elements are employed.
Some countries are content to provide banknotes with metal strips
which come out black on a photocopy. Although this prevents them
from being photocopied, elements of this type are very easy to
imitate. In contrast to this, there are also more complex
authentication elements, for example holograms and cinegrams.
Authentication elements of this type are based on the diffraction
of light by gratings and need to be observed under different
viewing angles in order to verify their authenticity. These
diffracted elements produce three-dimensional images, colour
variations or kinematic effects which depend on the angle of
observation and have to be checked on the basis of predetermined
criteria or rules. It is not practically possible to use machines
for reading information, for example images or numbers, encoded
using this technique. Furthermore, the information content of these
elements is very limited, and only an optical specialist will be
capable of discriminating definitively between forgeries and an
original.
[0005] A further consideration with diffractive optical effects is
that these have also been used for consumer articles such as
wrapping paper, toys and the like. The relevant production methods
have therefore become widely known and are correspondingly
straightforward to imitate.
[0006] Further to the diffractive elements mentioned above, other
components are also known which are suitable for optimum copy
protection. These include optical components, as disclosed for
example by EP-A-689084 or EP-A-689065, that is to say components
with an anisotropic liquid-crystal layer, which latter has local
structuring of the molecular orientation.
[0007] These components are based on a hybrid layer structure which
consists of an orientation layer and a layer which is in contact
with it and consists of liquid-crystal monomers or pre-polymers
cross-linked with one another. In this case, the orientation layer
consists of a photo-oriented polymer network (PPN)--synonymous with
LPP used in other literature--which, in the oriented state, through
a predetermined array, defines regions of alternating orientations.
During the production of the liquid-crystal layer structure, the
liquid-crystal monomers or pre-polymers are zonally oriented
through interaction with the PPN layer. This orientation which, in
particular, is characterised by a spatially dependent variation of
the direction of the optical axis, is fixed by a subsequent
cross-linking step, after which a cross-linked, optically
structured liquid crystal monomer or pre-polymer (LCP) with a
pre-established orientation pattern is formed. Under observation
without additional aids, both the orientation pattern itself and
the information written into the cross-linked LCP layer are at
first invisible. The layers have a transparent appearance. If the
substrate on which the layers are located transmits light, then the
LCP orientation pattern or the information which has been written
become visible if the optical element is placed between two
polarisers. If the birefringent LCP layer is located on a
reflecting layer, then the pattern, or the corresponding
information, can be made visible using only a single polariser
which is held over the element. LPP/LCP authentication elements
make it possible to store information, virtually without
restriction, in the form of text, images, photographs and
combinations thereof. In comparison with prior art authentication
elements, the LPP/LCP elements are distinguished in that the
authenticity of the security feature can be verified even by a
layman since it is not first necessary to learn how to recognise
complicated colour changes or kinematic effects. Since LPP/LCP
authentication elements are very simple, reliable and quick to
read, machine-readable as well as visual information can be
combined in the same authentication element.
[0008] However, there remains the risk that, in the course of time,
forgers will be able to master this technique.
[0009] In the components described above, one pictorial element is
present (whether visible or invisible).
[0010] It would be desirable to improve the security or
entertainment value of such a component.
[0011] According to the present invention, an optical component
comprises one or more retarder(s) in which are embedded a plurality
of images, the images being so arranged that, at any point in the
plane of the component, an element of not more than one image is
present, each image being associated with a different interaction
with polarised light. This association can be achieved in various
ways, for example, each image is embedded in patterned retarder(s)
(one or more), each of them having patterns with different optical
axis.
[0012] The invention also provides a viewing system, comprising a
source of polarised light, a component as set forth above, through
which the polarised light can travel, and an analyser (in practice,
a polarising sheet) for light which has traversed the component,
the analyser being rotatable about the axis of the direction of
travel of the light. The source of polarised light may be a
polarising sheet applied to the surface of the component.
[0013] The different images may be contained in successive parallel
stripes, each preferably narrower than the eye can resolve, into
which the surface area of the component is divided; if these are n
images, any one image will usually be represented on every nth
stripe.
[0014] Such an optical component has the surprising property,
valuable in the fields of entertainment, document authentication
and forgery countermeasures, that simply by rotating a polariser
(=the analyser), a plurality of different images, all visible in
ordinary light, can be seen one after the other. Previously, it was
possible to reveal only one hidden image in this way. However, all
the advantages of the "one hidden image" technology, as described
for example in EP-A-689065, PCT/IB98/00687 or CH 841/98, can be
maintained.
[0015] The invention will now be described by way of example with
reference to the accompanying drawings, in which:
[0016] FIG. 1 shows magnified a first optical component according
to the invention, manufactured with two retarders, in its
appearance when viewed through an analyser in the orientation
indicated in the Figure;
[0017] FIG. 2 shows the same component as FIG. 1, in its appearance
when viewed through an analyser in the orientation indicated in
FIG. 2, and
[0018] FIG. 3 shows the same component as FIG. 1, in its appearance
when viewed through an analyser in the orientation indicated in
FIG. 3 leading to the `negative` counterpart of the image shown in
FIG. 1;
[0019] FIG. 4 shows the same optical component as FIG. 1, in its
appearance when viewed through an analyser in the orientation
indicated in FIG. 4 leading to the `negative` counterpart of the
image shown in FIG. 2;
[0020] FIG. 5 shows a striped photo mask which includes the
information of picture I. This striped photo mask is needed for
(this example of) the production process of the optical
component.
[0021] FIG. 6 shows a striped photo mask which includes the
information of a second image, picture II. This photo mask is
optional in the production process of the optical component.
[0022] FIG. 7 shows a striped but otherwise completely unpatterned
photo mask, in other words including no picture information. This
striped photo mask is used in the production process of the optical
component.
[0023] FIG. 8 shows a photo mask which reflects picture II. This
mask does not include any stripes as shown in FIGS. 5, 6 and 7.
[0024] FIG. 9 shows the contrast dependence of each image (here 2
images) related to the analyser angle with respect the optical
component. The analyser angle is interrelated to the x-axis (when
the analyser is parallel to the x-axis then the angle is
0.degree.). At specific analyser angles peaks of maximum contrasts
are reached.
[0025] FIG. 10 shows the contrast dependence of each image (here 2
images) related to the analyser angle in case of a second optical
component according to the invention and described in the following
Figures, this second optical component being manufactured with 1
retarder. The analyser angle is interrelated to the x-axis (when
the analyser is parallel to the x-axis then the angle is
0.degree.). At specific analyser angles peaks of maximum contrasts
are reached.
[0026] FIG. 11 shows, magnified, the second optical component in
its appearance when viewed through an analyser in the indicated
orientation;
[0027] FIG. 12 shows the second optical component in its appearance
when viewed through an analyser in the indicated orientation
different from FIG. 11;
[0028] FIG. 13 shows a striped photo mask which includes the
`positive` (`positive` means dark information patterns on bright
background) information of picture I of the second optical
component.
[0029] FIG. 14 shows a striped photo mask which includes the
`negative` (`negative` means bright information patterns on dark
background) information of picture I.
[0030] FIG. 15 shows a striped photo mask which includes the
`positive` information of a second image, picture II.
[0031] FIG. 16 shows a striped photo mask which includes the
`negative` information of a second image, picture II. The photo
masks of FIGS. 13-16 are all needed in this example of the
production process of the optical component.
[0032] FIG. 17 shows schematically an optical component according
to the invention, working in the reflective mode.
EXAMPLE 1
[0033] An optical component according to FIGS. 1, 2, 3 and 4 is
made by applying a layer of suitable orientable linearly
photopolymerisable (LPP) material such as cinnamic acid derivatives
or ferulic acid derivatives illustrated for instance in patent
publications EP-A-611786, WO 96/10049 and EP-A-763552 to a
transparent substrate. This layer with a thickness of about 50 nm
is exposed through a photo mask, shown schematically in FIG. 5, to
polarised light of different polarisation directions. The photo
mask is of alternative adjacent opaque (II) and
in-principle-transparent (I) stripes which, when projected onto the
layer of LPP material, have a width of 1/8 mm each, which is
smaller than the eye can resolve. The stripes (I) are themselves
blacked out in parts, to leave the image of an upright cross. The
illumination sequence for this first LPP layer is shown in Table 3
with ultimate result shown in Table 1: the angle .alpha. of the
linear polarised light with a suitable wavelength in respect to the
x-Axis travelling through the bright picture areas of stripes I
(FIG. 5) is +13.5.degree. (illumination step 1); the picture
illustrated in FIG. 5 is an upright cross but any image can be
used. Then, this mask is replaced by the photo mask shown in FIG.
7. The opaque stripes (II) of both masks coincide, but the former
unexposed areas of stripes I of FIG. 5 will be now exposed at an
angle .alpha. of -13.5.degree. (illumination step 2); finally this
mask is removed and a third illumination step parallel to the
x-Axis (.alpha.=0.degree.) is applied to expose the stripes II of
FIG. 5 (illumination step 3). After these 3 illumination steps all
areas of the first LPP layer has been exposed to polarised light of
a suitable wavelength. These exposures cause polymerisation, in
respectively different preferred alignments.
[0034] Thereafter, this first LPP layer is coated with a
cross-linkable liquid crystal monomer or pre-polymer mixture (LCP)
which shows birefringence, such as LCP mixture M.sub.LCP described
in more detail later. (M.sub.LCP has an optical anisotropy .DELTA.n
of 0.13 leading to a film thickness of 1.5 .mu.m). The LCP material
adopts the alignment (if any) of the immediately underlying region
of the LPP layer. The whole is then exposed to unpolarised
(isotropic) light of a suitable wavelength to crosslink the LCP
material (illumination step 4 of Table 3).
[0035] Then, a second LPP layer (film thickness about 50 nm) is
coated directly on the former LCP layer. Similar to the first LPP
layer further 4 exposures (illumination steps 5 to 8 in Table 3) to
polarised light of a suitable wavelength are applied to this second
LPP layer: the angle .alpha. of the linear polarised light in
respect to the x-Axis travelling through the bright picture areas
of stripes I of the photo mask (FIG. 5) is +31.5.degree.
(illumination step 5). Then, this mask is replaced by the photo
mask shown in FIG. 7 and the former unexposed areas of stripes I of
FIG. 5 will now be exposed at an angle .alpha. of -31.5.degree.
(illumination step 6). Then, the current (FIG. 7) mask is replaced
by the photo mask without any stripes of FIG. 8; the picture II
illustrated in FIG. 8 is a diagonal cross but any image can be
used. The bright areas of stripes II which were not exposed yet are
illuminated with polarised light at an angle .alpha. of +45.degree.
(illumination step 7). Finally also this mask is removed and all
areas which were not exposed before are illuminated by polarised
light parallel to the x-Axis (.alpha.=0.degree.) (illumination step
8). These exposures cause polymerisation, in respectively different
preferred alignments.
[0036] Thereafter, this second LPP layer is coated with a
cross-linkable liquid crystal monomer or pre-polymer mixture (LCP)
which shows birefringence, such as LCP mixture M.sub.LCP (M.sub.LCP
has an optical anisotropy .DELTA.n of 0.13 leading to a film
thickness of 1.5 .mu.m). Again, the LCP material adopts the
alignment (if any) of the immediately underlying region of the LPP
layer. The whole is then exposed to unpolarised (no mask necessary)
light of a suitable wavelength to crosslink the LCP material
(illumination step 9).
[0037] The various retarder layers may have the same (as here) or
different optical retardations .DELTA.nd.
[0038] This completes the manufacture of the optical component,
which in normal light is transparent.
[0039] In use, the optical component will be examined for
authenticity in the following way.
[0040] It is placed on a light box emitting linearly polarized
light, and appears transparent in transmission.
[0041] To check it, it is viewed through a rotatable sheet carrying
a polarizing grating; such sheets are known as analysers.
[0042] In summary, because of the different modes of interaction of
the two images with polarised light, as the analyzer is rotated,
the upright cross (stripes I, FIG. 1) appears and disappears, to be
replaced by the diagonal cross (stripes II, FIG. 2), which also
disappears on continued rotation of the analyzer. It is easy to
verify whether or not a document of unknown authenticity displays
two different images when inspected this way. The dependence of the
contrast on the analyser angle is also represented in FIG. 9.
[0043] In more specific detail, the appearance of images depends on
various angles and retardation's as set forth in the following
tables, in which the symbols have the following meaning:
[0044] .delta..sub.1 Optical axis of first LCP layer;
[0045] .delta..sub.2 Optical axis of second LCP layer;
[0046] x-axis: Axis of polarising grating of inspection
arrangement; .alpha.=0.degree. means parallel to the x-Axis
[0047] x, y: colour co-ordinates indicate the position in the
Chromaticity Diagram; for example, stripes I in FIG. 2 appear grey
to brownish; the colour co-ordinates of these stripes are
calculated as x=0.3684 and y=0.3609 leading to such a slightly
coloured appearance described as brownish.
[0048] normed brightness: 1.000=brightness of inspection light as
viewed through polarisers and analyser arranged parallel, no
retarder present.
[0049] .DELTA.nd.sub.1, .DELTA.nd.sub.2 Optical retardations of the
LCP layers (.DELTA.nd.sub.1=.DELTA.nd.sub.2=0.2 .mu.m)
[0050] d.sub.1, d.sub.2: Thickness of LCP retarder layers
(d.sub.1=d.sub.2=1.5 .mu.m).
[0051] Table 2 shows calculated values of the feasible contrast
ratios and colours which can be achieved with the optical component
described in Example 1.
EXAMPLE 2
[0052] In another example according to the invention, it is
possible to make a similar secure component with only one retarder
layer. This component is examined for authenticity by the procedure
already described. Upon rotating the analyser, peaks of maximum
contrast are obtained at specific rotation angles, at each of which
a respective one of the (otherwise hidden) images becomes visible
(FIG. 10).
[0053] An optical component according to FIGS. 11 and 12 (their
`negative` counterparts are not shown here, but appear--similar to
Example 1--when the analyser angle to the x-axis is 0.degree. and
-45.degree., respectively) is made by applying a layer of suitable
orientable linearly photo-polymerisable (LPP) material such as
cinnamic acid derivatives or ferulic acid derivatives illustrated
for instance in patent publications EP 611786, WO 96/10049 and EP
763552 to a transparent substrate. This layer with a thickness of
about 50 nm is exposed through a photo mask, shown schematically in
FIG. 13, to polarised light of different polarisation directions.
The photo mask is of alternative adjacent opaque (II) and
in-principle-transparent (I) stripes which, when projected onto the
layer of LPP material, have a width of 1/8 mm each which is smaller
than the eye can resolve (same resolutions show masks illustrated
in FIGS. 14, 15 and 16). The stripes (I) are themselves blacked out
in parts, to leave the image of a character `3`. The illumination
sequence for this LPP layer is: the angle .alpha. of the linear
polarised light with a suitable wavelength in respect to the x-axis
travelling through the bright picture areas of stripes I (FIG. 13)
is +45.degree. (illumination step 1); the picture illustrated in
FIG. 13 is a character `3` but any image can be used. Then, this
mask is replaced by the photo mask shown in FIG. 14. This mask
is--except the opaque stripes II--exactly the `negative`
counterpart of the mask shown in FIG. 13. The opaque stripes (II)
of both masks coincide, but the former unexposed areas of stripes I
of FIG. 13 will be now exposed at an angle .alpha. of 0.degree.
(illumination step 2); then a third mask (FIG. 15) is applied
including the image information of picture II; the picture
illustrated in FIG. 15 is a character `4`, but any image can be
used. The angle .alpha. of the linear polarised light in respect to
the x-axis travelling through the bright picture areas of stripes
II of the photo mask (FIG. 15) is +22.5.degree. (illumination step
3). Then, this mask is replaced by the photo mask shown in FIG. 16
and the former unexposed areas of stripes II of FIG. 15 will now be
exposed at an angle .alpha. of +67.5.degree. (illumination step 4).
These exposures cause polymerisation, in respectively different
preferred alignments.
[0054] Thereafter, this LPP layer is coated with, a cross-linkable
liquid crystal monomer or pre-polymer mixture (LCP) which shows
birefringence, such as mixture M.sub.LCP (M.sub.LCP has an optical
anisotropy .DELTA.n of 0.13 leading to a film thickness of 1.5
.mu.m). The LCP material adopts the alignment (if any) of the
immediately underlying region of the LPP layer. The whole is then
exposed to unpolarised (no mask necessary) light of a suitable
wavelength to crosslink the LCP material (illumination step 5).
[0055] This completes the manufacture of the optical component,
which in normal light is transparent.
[0056] In use, the optical component will be examined for
authenticity in the following way.
[0057] It is placed on a light box emitting linearly polarised
light, and appears transparent in transmission.
[0058] To check it, it is viewed through a rotatable sheet carrying
a polarising grating; such sheets are known as analysers.
[0059] In summary, because of the different modes of interaction of
the various images patterns with polarised light, as the analyser
is rotated, the character `3`, (stripes I, FIG. 13) appears and
disappears, to be replaced by the character `4` (stripes II, FIG.
14), which also disappears on continued rotation of the analyser.
It is easy to verify whether or not a document of unknown
authenticity displays two different images when inspected this
way.
[0060] When placing or attaching the optical components described
in Examples 1 and 2 on top of a reflector which maintains the
polarisation direction of incident light, and when using a
polariser which is rotatable about the axis of the direction of
travel of the light which has traversed the polariser and the
optical component, such light is reflected at said reflector and
traverses a second time the optical component and said polariser
(schematically shown in FIG. 17). Then similar images as seen in
the transmissive mode illustrated in Example 1 and 2 are observed:
by rotating said polarizer, peaks of maximum contrasts for each
image are obtained at specific rotation angles of the polarizer,
enabling, at each such angle, visualisation of a respective image
not otherwise visible; the image appears bluish/white or
violet/whitish with relative poor contrasts because the optical
retardations and its optical axis were not optimised for the
reflective operation mode.
[0061] The production of a PPN (=LPP) and LCP layer which can be
used according to the invention will be described still by way of
example, in more detail below.
[0062] 1. Production of a PPN Layer
[0063] Suitable PPN materials are described for instance in patent
publications EP-A-611786, WO 96/10049 and EP-A-763552, such as
cinnamic acid derivatives or ferulic acid derivatives. For the
foregoing Examples, the following PPN material was chosen: 1
[0064] A glass plate was spin-coated with a 2 percent strength
solution of the PPN material in cyclopentanone for one minute at
2000 rpm. The layer was then dried for 5 to 10 minutes at
120.degree. C. on a hotplate. The layer was then exposed to
linearly polarized light, Hg high-pressure lamp for 20 to 405
seconds (depending on the strength of the lamp and on the number of
LPP/LCP layers of the optical component) at room temperature. The
layer was then used as an orientation layer for liquid
crystals.
[0065] 2. Mixture M.sub.LCP of Cross-Linkable LC Monomers for the
LCP Layer.
[0066] In the examples, the following diacrylate components were
used as cross-linkable LC monomers: 2
[0067] Using these components, a supercoolable nematic mixture
M.sub.LCP with particularly low melting point (Tm .about.35.degree.
C.) was developed, making it possible to prepare the LCP layer at
room temperature.
[0068] The diacrylate monomers were present with the following
composition in the mixture:
[0069] Mon180%
[0070] Mon215%
[0071] Mon25%
[0072] In addition a further 2% of the Ciba-Geigy photoinitiator
IRGACURE (trade mark) was added to the mixture.
[0073] The mixture M.sub.LCP was then dissolved in anisol. By means
of the M.sub.LCP concentration in anisol, it was possible to adjust
the LCP layer thickness over a wide range. Especially for the
examples of optical components described in this patent, desired
retardations .DELTA.nd of 0.2 .mu.m could be achieved.
[0074] For photoinitiated cross-linking of the LC monomers, the
layers were exposed to isotropic light from a xenon lamp for about
5 to 30 minutes (depending on the strength of the lamp) in an inert
atmosphere.
[0075] The optical effects described above, as well as the
corresponding layer structures and material compositions, represent
no more than a choice from many possibilities according to the
invention, and may in particular be combined in a wide variety of
ways in order to develop authenticating elements.
[0076] Thus, it is of course possible for any other kind of
birefringent layer than the LCP layer described to be used to
produce an optical effect that can be employed in optical
components, for example for authentication elements.
[0077] It is furthermore possible for the examples described above,
to use not a PPN orientation layer but a different orientation
layer which, according to the desired optical property and
resolution, has the same or similar properties to a PPN layer. It
is also conceivable to produce the orientation required for a
retarder layer using a correspondingly structured substrate. A
structured substrate of this type can for example, be produced by
embossing, etching and scratching.
1TABLE 1 Arrangement of the optical axis of the LCP layers and
optical appearance of the optical element. Optical Retardations
.DELTA.nd, and .DELTA.nd.sub.2 of the LCP-Retarder Layers
.DELTA.nd.sub.1 and .DELTA.nd.sub.2 = 0.2 .mu.m 3 4 5 6 7 8 Angle
of x axis to polariser 0.degree. 0.degree. 0.degree. 0.degree.
Angle of x axis to analyser 45.degree. 45.degree. 90.degree.
90.degree. Angle of x axis to .delta..sub.1 +13.5.degree. 0.degree.
+13.5.degree. 0.degree. Angle of x axis to .delta..sub.2
+31.5.degree. +45.degree. +31.5.degree. +45.degree. Normed
brightness 0.9925 0.5000 0.4859 0.8104 Colour co-ordinates x 0.3343
0.3334 0.3684 0.3062 y 0.3355 0.3333 0.3609 0.3186 Colour white
white whitish/brownish white Appearance of the pixel BRIGHT GREY
GREYISH BRIGHT 9 10 11 12 Angle of x axis to polariser 0.degree.
0.degree. 0.degree. 0.degree. Angle of x axis to analyser
45.degree. 45.degree. 90.degree. 90.degree. Angle of x axis to
.delta..sub.1 -13.5.degree. 0.degree. -13.5.degree. 0.degree. Angle
of x axis to .delta..sub.2 -31.5.degree. 0.degree. -31.5.degree.
0.degree. Normed brightness 0.0052 0.5000 0.5000 0.0000 Colour
co-ordinates x 0.2669 0.3334 0.3684 0.3334 y 0.1539 0.3333 0.3603
0.3333 Colour ca. violet white whitish/brownish white Appearance of
the pixel DARK GREY GREYISH DARK
[0078]
2TABLE 2 Contrasts 13 14 overall effect overall effect Point on
image BRIGHT GREY BRIGHT GREY BRIGHT BRIGHT Colour white white
.about.white whitish/brownish white .about.whitish Normed
brightness 0.993 0.500 0.747 0.486 0.810 0.648 Point on image DARK
GREY DARK GREY DARK DARK Colour ca. violet white .about.dark violet
whitish/brownish white .about.black Normed brightness 0.005 0.500
0.253 0.500 0.000 0.250 Maximum contrast 199:1 1:1 3:1 1:1
>200:1 2.6:1
[0079]
3TABLE 3 Sequence of illumination steps with linear polarized and
isotropic light to generate the optical component of Example 1
(picture in picture) 15 16
* * * * *