Background of the invention
This invention relates to an improvement of transparent and semitransparent
diffractive elements and more particularly to transparent and semitransparent type
holograms and their making process These diffractive elements are themselves transparent
or semitransparent in the visible (VIS) and/or near infrared (NIR) spectral regionsand
yet are also endowed with the characteristics of a reflection type element being
observed under suitable angle. It means that reproduction in the transparent or
semitransparent element of the present invention is effected only within a specific
reproduction angle range, while no hologram is recognised at other ordinary angles.
This leads to the advantage that there is no visual obstruction of the article
on which the diffractive element is laminated. Fig. 1 shows the basic constitution
of the transparent or semitransparent diffractive element according to the present
State of the art
Demand for holograms has grown not only as the way of the record of
sound or information but as the elements used in such activities of human beings
as advertisement, security sector, safety technique, protection of product originality,
money counterfeit protection etc.
It is well known that one of the following replication technologies
is usually used for mass production of any diffractive elements in suitable polymer
materials - hot embossing, injection moulding and casting.
Relief microstructure (master copy) is produced by one of the many
high resolution fabrication technologies, the most commonly used being holographic
exposure of suitable photosensitive material, including chalcogenides (US 3,825,317),
direct writing with focused laser and e-beam, optical photolithography with subsequent
wet or dry etching.
In most cases, a nickel shim or stamper is electroformed or replica
is produced through casting into epoxy resin. These replicas are used for own mass
production of copies into polymers using injection moulding (CD fabrication), casting
(production of gratings for spectrophotometers) or hot embossing, for example into
transparent foil (M.T. Gale; J. of Imaging Science and Technology 41 (3) (1997)
Transparent polymeric materials such as polyethylene with index of
refraction n = 1.5 - 1.54, polypropylene n = 1,49, polystyrene 1,6, polyvinyl chloride
1,52 - 1,55, polyester resin 1.52 - 1,57 etc. (for more examples see US patent
4856857) or copolymers (for correction of index of refraction) can be used for
transparent or semitransparent holograms and other diffractive elements production.
Low refraction index value of these polymers or copolymers prepared from them determines
their low reflectance (R about 4 %), hence the holographic effect of diffractive
structure developed in layers of these polymers is insufficient (US patent 4856857).
Under the term "holographic effect" used in the following text we will understand
the phenomenon, that the hologram is very intensive in reflected light at suitable
angle of observation. Low reflected intensity and thus the drawback of poor brightness
of diffractive element recorded in the polymer layer is usually passed by forming
a thin metallic film (generally Al) on the relief forming face of transparent polymeric
layer (M. Miler Holography - theoretical and experimental fundamentals and their
application, SNTL, Prague 1974 (in Czech); M.T. Gale: J. of Imaging Science and
Technology 41 (3) (1997)211).
Strong improvement of brightness achieved at the cost of loss of the
transparency is the main drawback of such technique. Transparency or at least semitransparency
of diffractive element is required or desired in many applications (for example
protective diffractive elements on banknotes, identity cards with photo etc.).
Some technical applications of diffractive elements are directly conditioned by
transparency or semitransparency of created element ( for example microlense array
for CCD cameras, polarising filters etc.).
It is further known that to preserve (or to decrease only partly)
the transparency of diffractive element and at the same time to improve holographic
effect of the hologram recorded in the polymeric layer (further called layer 1),
it is necessary to cover layer 1 by other transparent layer (further called layer
2) of different material (further called holographic effect enhancing material)
which has in general different index of refraction n (i.e. higher or lower ) than
material of the transparent layer 1 (US patent 4856857, US patent 5700550, US patent
5300764). The higher difference in index of refraction of polymeric bearing layer
1 and holographic effect-enhancing layer 2, the higher holographic effect can be
achieved (US patent 4856857).
It is as well known that very thin layer (with thickness to the limit
20 nm) of suitable metal (e.g. Cr, Te, Ge) can be used as such layer 2 deposited
on the transparent layer 1 in which a hologram has been hot-formed. Such very thin
metallic layer being used, relatively high transparency is preserved. Relatively
strong enhancing of holographic effect can be achieved when the index of refraction
of deposited metallic layer is either significantly lower (e.g. Ag n = 0,8; Cu
n 0,7) or significantly higher (e.g. Cr n = 3,3, Mn n = 2,5, Te n = 4,9) than index
of refraction of transparent layer 1 (n about 1,5), (US patent 4856857). Such thin
metallic layers are deposited at transparent, diffractive element bearing layer
1 by vacuum deposition technique. The drawback of the application of thin metallic
layer as holographic effect enhancing material is relatively high melting point
of these materials and therefore difficult evaporating of many of these metals.
An additional drawback is high absorption coefficient of metals. Already slight
deviations in the thickness of evaporated metal layer implicate significant deviations
in the transmissivity of the system (layer 1 - bearing diffractive element + layer
2 - metal) and moreover upper limit of the permissible thickness is very low (it
depends on the metal, but in general it must not exceed 20 nm (US patent 4856857)).
According to our measurements evaporation of either 10 nm thick Cr layer or 4 nm
thick Ge layer on the polymeric layer decreases its transmissivity down to about
30 % (see Fig. 2).
In the present art, oxides of metals (e.g. ZnO, PbO, Fe2O3,
La2O3, MgO etc.), halogenide materials (e.g. TICl, CuBr,
CIF3, ThF4 etc.) eventually more complex dielectric materials
(e.g. KTa0,65Nb0,35O3, Bi4(GeO4)3,
RbH2AsO4 etc.) are used single or possibly in several layers
deposited criss-cross as holographic effect enhancing layers (US patent 4856857).
The drawback of the application of these materials is the fact that their index
of refraction values are very close to the index of refraction of transparent polymeric
layer 1 (e.g. index of refraction values are 1,5 for ThF4, 1,5 for SiO2,
1,6 for Al2O3, 1,6 for RhH2AsO4 etc.)
(US patent 486857). Accordingly an amplification of holographic effect is relatively
low. Many of these materials require again relatively high temperature for their
evaporation and not least some of them are quite expensive or hardly prepareable,
what obstructs their mass application.
Further it is known, that binary chalcogenides of zinc and cadmium
as well as compounds Sb2S3 and PbTe (US patent 4856857),
eventually multilayer systems of these chalcogenides with oxides or halides (US
patent 5700550) or multilayer system ZnS and Na3AlF6 (US
patent 5300764) can be used as holographic effect enhancing. These materials are
endowed with satisfactory index of refraction values (e.g. 3,0 for Sb2S3,
2,6 for ZnSe, 2,1 for ZnS). But short wavelength absorption edge of many of these
materials (e.g. Sb2S3, CdSe, CdTe, ZnTe) lies within near
IR region only and these materials are characterised by high values of absorption
coefficient in VIS. Similarly with metal layer used as layer 2, only very thin layers
of these materials can be used as holographic effect enhancing layer 2 to achieve
at least semitransparency of final product. Transparency is again significantly
influenced by thickness deviations. Additional significant drawback of these materials
is their difficult vaporization (again similarity with metals) given by their high
values of their melting points Tg alfa - ZnS 1700 °C, beta - ZnS 1020
°C, ZnSe >1100 °C, ZnTe 1238 °C, CdS 1750 °C, CdSe > 1350 °C, CdTe 1121 °C,
PbTe 917 °C) (Handbook of Chemistry and Physics 64th Edition 1983/84).
In the present art the process according to the scheme given in Fig.
3 is usually used in the mass production of transparent diffractive elements. Firstly
a diffractive pattern is made in the layer 1, after it a thin dielectric or metallic
layer is evaporated (perpendicularly or under specific incidence angle) a subsequently
this evaporated layer is overlapped or laminated by another polymeric layer (M.T.
Gale: Joumal of Imaging Science and Technology 41 (3) (1997) 211). As above mentioned
materials (metals, their oxides, halides, binary chalcogenides of Zn and Cd, Sb2S3
and PbTe) are used as layer 2 in the production of diffractive elements by this
way, the method has the same drawbacks, e.g. high melting temperatures determine
difficult deposition, even small deviations in the thickness cause large deviations
in the transmissivity, comparable index of refraction of many of these materials
with index of refraction of polymeric layer 1, eventually full non transparency
Further it is known that holographic tape (relief phase holograms
shaped in a vinyl tape) have improved scratch resistance being covered with such
materials as waxes, polymers and inorganic compounds, besides others arsenic sulphide
can be used (US patent 3 703 407). In addition the coating enables tapes to be
lubricated and enables tapes to be used in a liquid gate tape transport mechanism.
In order to maintain the same diffraction efficiency as an uncoated tape, the minimum
depth of this coating must be greater than the maximum peak-to-valley depth of
any corrugation (US patent 3 703 407).
The document US 4 856 857 discloses a diffractive transparent element
consisting of at least two layers having different refractive indices. The first
layer is a transparent polymer in which a diffraction pattern is formed. The second
layer enhances the holographic effect, has a higher refractive index than the
first layer, comprises chalcogenides and sulphur, and has a melting point of about
This document also discloses a corresponding production method.
The features of the preambles of independent claims 1, 4 and 5 are
knonw in combination from this document.
Subject matter of the invention
The present invention does away with the drawbacks of the present-day
techniques of transparent and semitransparent diffractive elements production.
Transparent and semitransparent diffractive elements, particularly
holograms, consisting at least of two layers with different index of refraction,
whereof a first bearing layer (1) is a transparent polymer or copolymer having
index of refraction lower than 1,7 and on said first bearing layer is deposited
a second to exposure sensitive holographic effect enhancing high refraction index
layer (2) constituted by substances based on chalcogenides with an index of refraction
higher than 1,7 and a melting temperature lower than 900 °C, characterized in that
the first diffractive pattern is mechanically shaped in the bearing layer (1) and/or
in the the high refraction index layer (2) and at least one further second diffractive
pattern is formed in the exposure sensitive high refraction index layer (2) constituted
by substances based on chalcogenides comprising at least one of the elements from
the group sulphur, selenium, tellurium, said chalcogenide based substances being
selected from the group of binary, ternary and even more complex chalcogenide and/or
chalcohalogenide systems, containing, in addition to S or Se or Te, as a more electropositive
element some of the elements Cu, Ag, Au, Hg, B, Al, Ga, In, Tl, Si, Ge, Sn, Pb,
N, P, As, Sb, Bi.
Chalcogenides based matters can contain further transient metal and/or
at least one rare earth element, e.g. Pr, Eu, Dy.
Transparent or semitransparent diffractive element can further consists
of other layers e,g. protective layer, adhesive layer, fragile layer, anchor layer.
Protective layer protects layer 2 or layer 1 against environmental effect or against
undesirable effect of consecutive exposure by UV light and improves tesistivity
of the final product. The layer can either be permanent part of the hologram or
of the diffractive element or can be removable. Adhesive layer allows unrepeatable
or repeatable anchoring of the hologram or other diffractive element on protected
article, printed document etc. The function of fragile layer is to adhere the upper
layer and the lower layer and yet effect destruction of diffractive element during
peeling for the purpose of forgery. Anchor layer is used to improve adhesivity
of diffractive element to the base supporting sheet or to releasable sheet in the
case of application as seal, sticker, label etc.
Transparent layer 1 can be inseparable part of some larger product,
in such case the high refraction index layer 2 can be for example sprayed on the
Production processes of such transparent and semitransparent diffractive
elements are defined in independent claims 4 and 5.
If the depth of diffractive pattern is greater than the thickness
of high refraction index layer 2 (very common situation), practically identical
product (Fig. 1) is obtained as when the previous procedure is used. If the embossing
depths are lower than thickness of high refraction index layer, the layer 1 operates
as carrier of high refraction index layer 2 only. After that the second diffractive
patterns are formed in the said to exposure sensitive high refraction index layer
High refraction index layer can be deposited on a previously coloured
layer 1 and thus through the combination of their colours (colour of layer 2 depending
on the composition and thickness used) a required colour effect of transparent
or semitransparent diffractive element can be achieved.
High refraction index layer 2 can be deposited either at low pressure
e.g. using vacuum evaporation, sputtering or chemical vapour deposition (CVD) technique
or at normal pressure as solution of chalcogenide based matters using e.g. spraying,
painting or spin coating method.
The composition of high refraction index layer 2 formed with some
chalcogenide based matters can be modified by exposure or annealing induced diffusion
of metals and/or by halogens and/or oxygen, which are implanted into layer 2 by
interaction of the layer 2 with halogen vapours or oxygen or by air hydrolysis.
The sensation of the first diffractive pattern shaped mechanically
in layer 1 and/or layer 2 is modified by second diffractive pattern formed in layer
2 by exposure and/or annealing and/or by selective etching.
Exposure with radiation of suitable wavelength and intensity (values
depend on the particular composition of high refraction index layer (2), e-beam,
ions, X-ray radiation etc.) or annealing originates structural changes in high
refraction index layer or it originates even changes in its chemical composition
(e.g. diffusion of metal, which is in direct contact with high refraction index
layer, hydrolysis, oxidation). Thereby a change of the value of index of refraction
of layer 2 takes place (it usually increases) and thus the difference between values
of index of refraction of bearing layer 1 and high refraction index layer 2 is
modified. It results in a different optical perception of the product. A chemical
reaction induced by exposure or by annealing, e.g. with surrounding atmosphere,
can result in the transformation of chalcogenide material into fully different
compound (e.g. oxide); the product of such reaction must again satisfy the condition,
that its index of refraction is higher than 1,7.
Local exposure through the mask or holographic exposure or local annealing
can produce a record of the further second diffractive pattern into the high refraction
index layer 2; the record can be either amplitude (based on different absorption
coefficient of exposed and unexposed part of layer 2) or phase type based on either
different values of index of refraction of exposed and unexposed parts of layer
2 or based on different thickness of exposed and unexposed parts of the layer 2
(different thickness can be achieved not only directly during exposure but also
by consecutive etching of layer 2 by using well-known methods); even here can be
used the phenomenon of local photoinduced diffusion, hydrolysis, oxidation etc.
and the matter of high refraction index layer 2 can, in the place of local exposure
or annealing change its chemical composition; resulting record in the high refraction
index layer 2 can partly modify visual perception of the hologram and In addition
it can be seen in view-through.
As index of refraction values of majority of chalcogenides exceed
the value n = 2, application of chalcogenides layers as holographic effect enhancing
layer 2 deposited on the transparent polymeric layers 1 with n < 1,7 results
generally in a significant visual perception.
The transparency of final hologram or other diffractive element can
be influenced through the thickness of layer 2.
Another important advantage of chalcogenide materials is the fact,
that they can be synthesised in many systems in amorphous state and their glass
forming regions are relatively wide. Being amorphous, these materials have not
only very low scattering losses, but the possibility to prepare even nonstochiometric
compounds takes place. Gradual mutual substitution of elements (not only S, Se
and Te) in the composition of amorphous chalcogenides causes continuous changes
in their index of refraction and reflectivity. Thus enhancement of holographic
effect can be "tailored".
As a result of gradual mutual substitution of elements in the composition
of amorphous chalcogenides arise gradual changes of their optical gap Egopt
values (e.g. As40S60 Egopt = 2,37 eV.
As40S40Se20 2.07 eV, As40Se60
1,8 eV) followed by gradual changes in the position of short wavelength absorption
edge. Thus the colour (for given thickness) of layer 2 can be changed as well and
transparent and semitransparent systems of different colours endowed with high
holographic effect can be produced. So even colourless polymeric layers 1 can be
used for production of transparent or semitransparent diffractive elements of required
colour using one (or more) chalcogenide based layer of suitable composition as
a layer 2. Thus composition and thickness of chalcogenide layer 2 influence significantly
the transparency of final product (hologram) (Fig. 4) and reflectivity (Fig. 5)
and thus intensity of holographic perception (it increases with the reflectivity
of layer 2).
Amorphous chalcogenides are mainly as thin layers photosensitive to
exposure with radiation of suitable intensity and vawelength (given by composition
of the layer), e-beam, ions etc. This property enables us to provide an supplementary
correction of index of refraction, reflectivity and transmissivity of high refraction
index thin layer using exposure induced structural changes (Fig. 6), by exposure
induced reaction of photosensitive chalcogenide layer with metal (e.g. Ag) (Fig.
6) or with gas (O2, air humidity) induced transformation into different
chemical substance, which must satisfy the condition that n > 1.7. Similar effect
can be achieved by annealing.
If exposure or annealing are local only, procedures mentioned in the
previous paragraph can result in the formation of an image (including holographic
one) in the high refraction index layer, which can partly modify visual perception
of the hologram and in addition it can be seen in view-through. Sectional views
of structures developed using photoinduced structural changes and photoinduced
metal diffusion are presented in Fig. 7 and 8.
Further advantage of above mentioned chalcogenides are their low melting
temperatures (usually 100 - 300 °C). They can be therefore deposited by worldwide
commonly used vacuum evaporation method. As the values of absorption coefficient
in the region behind short vawelength absorption edge are low, even possible small
deviation in the thickness influences much less the holographic effect enhancing
than when thin metallic layers are used. Large areas of chalcogenide layers can
be formed relatively easily using corresponding vacuum evaporation equipment. The
thickness of the chalcogenide layer 2 can be adjusted by synchronising the evaporation
rate with the feed speed of transparent bearing layer 1.
Further advantage of amorphous chalcogenides is the fact, that mass
production of chalcogenides of many compositions exist worldwide and they are thus
immediately commercially available at affordable price.
Brief description of the drawings
Examples of design
- Fig. 1 Sectional view of the diffractive element of the present invention, 1
-transparent bearing polymeric layer with n1 < 1,7, 2 - high refraction
index chalcogenide based layer with n2 > 1,7
- Fig. 2 Optical transmissivity T and reflectivity R of holograms produced by
deposition of thin high diffractive index layer 2 formed by Cr or Ge on polyethylene
layer 1 with hot embossed diffractive pattern
- Fig. 3 Sectional views of sequence creation of transparent diffractive element
based on the possibility of creation a diffractive pattern in bearing layer 1 and
exploiting of the difference in index of refraction of layers number 1 and 2.
- Fig. 4 Optical transmissivity of holograms produced by deposition of thin high
diffractive index layer 2 formed by selected chalcogenide materials on polyethylene
layer 1 with hot embossed diffractive pattern
- Fig. 5 Reflectivity of holograms produced by deposition of thin high diffractive
index layer 2 formed by selected chalcogenide materials on polyethylene layer 1
with hot embossed diffractive pattern
- Fig. 6 Changes in optical transmissivity T of holograms created by photoexposure
and by diffusion of Ag according to the techniques described in example 2 and 3.
- Fig. 7 Sectional views of sequential steps of creation of transparent hologram
or other diffractive element based on the possibility of creation of a diffractive
pattern in bearing layer 1, exploiting the difference in index of refraction of
layers number 1 and 2 and the photosensitivity of high refraction index chalcogenide
- Fig. 8. Sectional views of sequential steps of creation of transparent hologram
or other diffractive element based on the possibility of creation a diffractive
pattern in bearing layer 1, exploiting the difference in the index of refraction
of layers number 1 and 2 and 5 (n1, n2 n5) and
the photoinduced diffusion of metal 4 into chalcogenide layer 2 leading to origin
metal doped high refraction index chalcogenide layer 5.
- Fig. 9. Sectional view of possible final product - transparent hologram transfer
sheet, which once being stuck on the protected article can not be peeled off without
Following examples are given for better understanding of the present
invention. Transparent polyethyleneterephthalate foil (n = 1,58) with thickness
50 µm or polycarbonate foil (n = 1,59) with thickness 60 µm were employed as layer
1 satisfying condition n < 1,7. Diffractive patterns were stamped into these
layers using Ni shim and hot embossing method. Holograms and other diffractive
elements, which were characterised by very low holographic effect, were further
treated by some of the following processes given in examples 1 to 6. Application
of thin chalcogenide layer as holographic effect enhancing, high refraction index
layer 2 (Fig. 1) is the common vein in all these examples. The possibility to modify
hologram or another diffractive element prepared by technique given in example
1 using well known phenomenon of photoinduced changes of the structure and properties
of chalcogenides used as high refraction index layer 2 is demonstrated in examples
2 - 4. Example 7 is demonstration of relief pattern production by stamping or pressing
the pattern into system polymeric layer 1 - chalcogenide high refraction index
layer 2 created in advance. All methods of fabrication of holograms or other diffractive
elements fabrication given in Examples 1 - 7 can be used for production of more
complicated final products, sectional view of one of them is given in Fig. 9. Example
of one simpler application of transparent holograms is given in the Example 8.
Example 1 (not claimed)
Thin layers (d = 10 - 500 nm) of Ge30Sb10S60
composition (n = 2,25) were deposited by vacuum evaporation method (deposition
rate 1 nm/sec, pressure 5.10-4 Pa) on bearing layer 1 from the side
of relief pattern fabricated beforehand in layer 1. In all cases sufficient holographic
effect has been achieved as a result of a greater reflected light intensity. Relatively
high transparency of prepared system has been preserved. Reflectivity (Fig. 5 curves
1,2) and transmissivity (Fig. 4 curves 2, 5 and Fig. 6 curve for d = 30 nm) of obtained
structures depend on the thickness of deposited high refraction index layer 2.
Thicker layers (of the order hundreds nanometers) being used, spectral dependence
of the optical transmissivity and reflectivity was influenced strongly by interference
phenomena, as vawelength of VIS and NIR radiation is comparable with thickness
of high refraction index layer 2.
Similar results were obtained when other chalcogenide materials, e.g.
Ge20Sb25Se55 (n = 3,11), As50Ge20Se30
(n = 2,95), (As0.33S0.67)90Te10 (n=
2,3) were applied as layer 2. Results of application of further chalcogenide based
systems Ag8As36.9Se55,1, Ge20Sb10S70,
as layers 2 satisfying condition n > 1,7 are given in Fig. 4 - 6. Similar results
were achieved when other binary (e.g. Se90Te10, Ge33S67),
ternary (e.g. (As0.33S0.67)95I5) or
even more complicated (e.g. As40S40Se10Ge10)
chalcogenides were applied as layer 2. Thin layers of more complicated systems
can be prepared either by vacuum evaporation of bulk samples of the same composition
or by simultaneous evaporation of more simple chalcogenides from two boats (e.g.
As40S60, Ge33S67, As40Se60
etc.). Enhancement of holographic effect has been achieved as well when chalcogenide
layers were deposited sequentially, e.g. two different holographic effect enhancing
layers were deposited sequentially. Thin layers of some chalcogenides (mainly of
sulphides, e.g. Ge33S67) are relatively unstable in the air
and can be hydrolysed, thus oxygen can be built in their structure.
Even thus hydrolysed layers operate as holographic effect enhancing
Thin layer AS42S58 with thickness 100 nm was
deposited by technique presented in example 1 on the carrying layer 1. Thus a significant
holographic enhancing effect was achieved and the hologram recorded in carrying
layer 1 was clearly visible under suitable angle of observation.
The system prepared by this way was modified using above described
phenomenon of photoinduced structural change in high refraction index layer 2 (where
exposed, the layer is transformed into a state marked as number 3 in Fig, 7). Exposition
of the system from the index of refraction layer 2 side by UV lamp (I = 18 mW/cm2)
for 300 sec caused a changed optical transimissivity of the system (Fig. 6) accompanied
with increase of index of refraction value for about 0,1 and thus holographic effect
was enhanced as well. Local exposure through the mask caused only local changes
in the transmissivity and index of refraction (layer 3 in Fig.7) and thus a negative
picture (exposed parts are less transparent) of used mask was developed in As42S58
layer, which can be seen in view-through and modifies the optical perception of
the hologram recorded in the layer 1 when this is observed in reflection.
Similar results were achieved when after deposition of As42S58
layer, still before its exposure, the system layer 1 - layer 2 was treated in iodine
vapours, what transformed composition of layer 2 into As-S-I (real composition
depends on the temperature and concentration of I2). Even without subsequent
exposure chalcohalide As-S-I layer had an enhanced holographic effect.
Thin Ge30Sb10S60 layer with thickness
30 nm and subsequently 10 nm thin Ag layer (layer 4 in Fig. 8) were deposited by
technique presented in example 1 on carrying layer 1. Consecutive 300 sec exposure
with Xe lamp (I = 20 mW/cm2) induced diffusion of Ag into Ge30Sb10S60
which was local only when exposition was provided through the mask (new composition
layer Ag-Ge30Sb10S60, marked as layer 5 in Fig
8). New Ag-Ge30Sb10S60 layer has generally a higher
value of index of refraction than Ge30Sb10S60 layer,
final value depending on the amount of diffused silver. Excessive, unreacted Ag
was striped by dipping in diluted HNO3
(1:1) and thus the picture of the
mask was recorded into original layer 2. This picture can be seen in view-through
and modifies optical perception of the hologram recorded in the layer 1 when this
is observed in reflection.
Final product fabricated in example 3 was further immersed in 0,02
mol/l KOH solvent, in which only high refraction index layer 2 is partly soluble.
Layer 5 is resistant against this solvent. Thus a relief picture is formed in chalcogenide
layer which can be seen in view-through and which again modifies optical perception
of the hologram recorded in the layer 1 when this is observed in reflection.
Example 5 (not claimed)
Thin layer (d = 40 nm) of Ge24.5Ga10.2S64.8Pr0,35
was deposited by vacuum evaporation method (deposition rate 1 nm/sec, pressure
5.10-4 Pa) on the bearing layer 1 from the side of relief pattern fabricated
beforehand in layer 1. Application of these materials as a high refraction index
layer resulted again in the enhancement of the holographic effect, e.g. hologram
recorded in carrying layer 1 was well seen when observed under specific angle.
Example 6 (not claimed)
Thin As40S60 layer was deposited using spin
coating method at normal pressure on the polycarbonate bearing layer 1 from the
side of relief pattern fabricated beforehand in layer 1. Starting solution As40S60
in n-propylamine was used in concentration 0,8 mol/l. Thicknesses of prepared layers
were in range 0,5 - 2 µm. Deposition of As40S60 layer again
led to partial improvement of optical perception of the hologram recorded in the
layer 1 when this was observed in reflection.
Similar results were achieved when solutions of As33S67
or AS40S60 in n-propylamine or triethylamine were used either
for spin coating deposition or these solvents were only painted on bearing layer
Thin As35S65 layer (d = 30 nm) was deposited
by vacuum evaporation method on polycarbonate bearing layer 1. Relief structure
was stamped into this bilayer from the side of high refraction index layer 2 by
hot embossing at temperature about 150 °C. After a couple of minutes at this temperature,
the whole system was cooled down and only after that thrust released. The product
had similar properties as when As35S65 layer of identical
thickness was used to prepare hologram by the technique described in Example 1.
An identical result was achieved when As35S65 layer was deposited
on layer 1 by CVD method.
Examples 8 (not claimed)
Thin layers (d = 20 nm) of Ge30Sb10S60
composition (n = 2,25) was deposited by vacuum evaporation method (deposition rate
1 nm/sec, pressure 5.10-4 Pa) on bearing layer 1 from the side of relief
pattern beforehand fabricated in layer 1. Obtained hologram was set on document
with text and photo (which had to be protected by applicated transparent hologram)
and sealed with the document into 175 µm thick polyester foil provided with fusible
paste. With regard to high transparency of the hologram (45% - 85 % in spectral
region 400 - 750 nm, see Fig. 4 curve 5) were both, text and photo, very well readable
and at the same time with regard to high reflection (24-15%, Fig. 5 curve 2) the
hologram formed in the bearing layer 1 was very well seen being observed under
Similar results (with different level of transparency and holographic
effectiveness depending on the composition and thickness of layer 2) were obtained
when other holograms endowed with enhanced holographic effect caused by application
of chalcogenide thin layer 2 prepared by methods presented in examples 1 - 7 were
used as counterfeit protecting elements.
Example of one diffractive structure which can be prepared is given
in Fig. 3 (including processing) and an example of one possible multilayer hologram
is presented in Fig. 9, where 6 stands for protecting layer which protects a high
refraction index layer 2 or bearing layer 1 against environmental effect or against
undesirable effect of consecutive exposure by UV light and improves resistivity
of the final product, 7 stands for adhesive layer which enables either unrepeatable
or repeatable anchoring of the hologram or other diffractive element on the protected
article, 8 stands for fragile layer which ensures good adherence of two layers
to each other and which depreciates itself during any attempt to peel off and thus
causes irreversible deformation and destruction of the diffractive element, 9 stands
for the anchor layer, which is usually used to improve adherence of adhesive layer
7 to high refraction index layer 2 or to the bearing layer 1. 10 stands for adhesive
layer providing clutching of hologram to the carrier 11 before its own application.
The present invention is applicable for fabrication of transparent
and semitransparent diffractive elements and more particularly to a transparent
and semitransparent type holograms. Besides of technical applications (e.g. record
of picture or information) these products can be used in such activities of human
beings as advertisement, security sector, safety technique, protection of product
originality, money counterfeit protection etc.