Note: Descriptions are shown in the official language in which they were submitted.
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Paper of value and method for producing it
This invention relates to security papers and papers of value, in particular
bank
notes, having a security element and provided with a dirt-repellent protective
layer,
and to a method for producing said papers of value.
Security prints, such as bank notes as well as shares, bonds, documents and
vouchers, checks, high-quality admission tickets, identification documents and
passports, are provided with elaborate printed images to increase their
forgery-
proofness, using sophisticated and limitedly accessible printing processes,
such as
intaglio, at least for individual parts of the images. Papers of value are
additionally
equipped with so-called security elements that are difficult to imitate and
permit even
laymen to check the authenticity of the paper of value. Such security elements
may be
for example window security threads visible in certain areas on the surface of
the
paper of value, applied foils having a transparent or metalized embossed
hologram,
blind embossings, so-called "latent images" produced by printing technology or
by
printing and embossing technology and rendering different information at
different
viewing angles, prints containing optically variable pigments and appearing in
varying colors at different viewing angles, or prints of metallic effect inks
having
metallic luster in a gold, silver, or bronze tone for example. The security
elements
may be already incorporated in or applied to the starting material, for
example paper,
of the paper of value, or produced between or after further processing steps
of the
paper of value, depending on the embodiment.
It is known to provide papers of value with dirt-repellent protective layers
to
extend their life and fitness for circulation. EP 0 256 170 B2 proposes for
example
providing printed bills with a protective layer containing cellulose ester and
micronized wax and applied to the bills all over.
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Common protective lacquer layers frequently have the disadvantage that their
surface is very smooth and glossy, which causes problems both in the
production and
processing of the papers of value and in the machine checking of the papers of
value
by means of optical sensors. Furthermore, conventional protective lacquer
layers
frequently have an adverse effect on the visual appearance of security
elements.
The problem of the invention is to propose a long-lived paper of value and
method for producing it that permit troublefree processing of the papers of
value and
their checking by means of optical sensors while simultaneously guaranteeing
that the
security elements are readily perceptible visually.
This problem is solved according to the invention by the features of the
independent claims. A still unprinted or already printed paper of value is
equipped on
at least one side with a protective layer formed by a matt lacquer or a thin
plastic foil
with a matt surface, said protective layer being interrupted, i.e. omitted, in
the area of
a security element. Since the predominant portion of the surface is covered
with a
protective layer, the paper of value is protected by the dirt-repellant
properties of the
lacquer layer or foil, while forming the protective layer surface of matt
lacquer or as a
matted foil permits reliable handling and processing of the papers of value
due to the
microroughness. It is also possible to apply a matt lacquer to the side of a
thin plastic
cover foil ending up on the outside and to laminate said foil to the paper of
value.
While papers of value with smooth protective lacquering or foils tend to slip
easily when being deposited, stacked and grasped, matt protective layers have
the
advantage of a better grip and are therefore easier and safer to handle.
Furthermore,
protective lacquering with matt lacquer has the advantage of retaining the
users'
accustomed perception of the papers of value by the sense of touch, while very
smooth coatings have an adverse effect not only on the haptic impression but
also on
the accustomed optical impression of a paper of value due to the glossy or
even
"greasy" appearance. A matt protective layer furthermore causes much less
reflection
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than usual glossy protective layers, thereby permitting troublefree machine
checking
of the papers of value with the optical sensors customarily used.
In the area of a security element, however, the matt protective layer is
interrupted. This avoids negative and dimming properties that a matt-lacquer
or foil
coating can have on the visual perception of a security element. Many security
elements, such as metalized embossed holograms which are applied to a paper of
value as an applied foil, or pigments of crosslinked liquid crystals embedded
in
resistant polymer layers, already have a protective and dirt-repellent surface
to begin
with. An additional matt protective layer would weaken their visual effect and
reduce
their brilliance without substantially improving the protection of such
security
elements.
If the attention of the user of a paper of value is to be directed
specifically to a
security element, however, it is advantageous to apply a protective layer
consisting of
gloss lacquer to the partial area of the paper-of-value surface where the
security
element is located and where the matt protective layer has been omitted.
Security
elements that are not glossy to begin with, or whose gloss is to be
strengthened, can
be thereby enhanced optically and emphasized visually. This also makes it
easier for
the unpracticed user to find the security elements in the paper of value. A
surface is
usually perceived as glossy when it has structural inhomogeneities whose
dimensions
are in the range of the light wavelength or less. In particular in cases where
the
security element does not already have a protective outer layer, as usually
with
applied foils, the life of the security element is also extended by the gloss
lacquer
layer applied thereover. This holds in particular for metallic effect ink
prints, but also
for blind embossings and so-called "latent images" executed by printing
technology,
which are subject to strong soiling and abrasion without a protective lacquer
cover.
The strikingness and visual effect of the partial area of the protective
lacquer layer
executed with gloss lacquer can be further increased by adding optically
variable
pigments to the gloss lacquer. These are largely transparent pigments that
produce a
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striking interplay of colors varying with the viewing angle. Some examples are
pearlescent pigments, thin film pigments such as so-called "Iriodin ", or
crosslinked
liquid crystal polymers.
Improved checkability of the papers of value is also obtained by mixing so-
called feature substances into the gloss lacquer provided for partial
lacquering. These
are substances that are uniquely checkable and detectable due to special
physical
properties like magnetism, wavelength-selective absorption, luminescence or
electric
conductivity. Particularly preferred feature substances are ones that can also
be
checked by the paper-of-value user without any great equipment expense but
nevertheless not be forged or only with enormous effort. Some examples are
special
fluorescent or phosphorescent substances that can be excited only within
narrow
wave ranges for example.
The inventive paper of value is preferably made of paper, for instance so-
called
"security paper" as is usual in bank-note printing and has a special feel and
sound.
The paper of value can be printed with any desired signs, including any
symbols,
printed images and patterns. The present invention can be applied especially
advantageously to paper substrates that have been printed by intaglio. For
high-
quality prints this printing process requires substrates with sufficient
surface
roughness to guarantee reliable and clean ink transfer from the printing plate
to the
substrate to be printed. The high pressure with which the substrate is pressed
against
the printing plate causes the paper surface to be greatly compacted and
smoothed in
the unengraved, i.e. non-ink-carrying, areas of the printing plate. This can
give rise
even on uncoated paper substrates to an undesirable gloss, which can be
reduced by a
subsequently applied matt lacquer protective layer. The invention is not
limited to
paper substrates, however, but can fundamentally also be transferred to
plastic and
composite materials, which are now being increasingly used in security
printing.
Composite materials are for example multilayer substrates having layers of
plastic
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and paper. A further variant consists of mat-like layers containing both
cellulose or
cotton fibers and plastic fibers.
The protective function of the protective lacquer layer or foil relates in
particular to its ability to repel dirt and increase moisture and abrasion
resistance. The
protective layer is expediently applied on both sides, i.e. the front and
back, of the
paper of value. For matt execution of the protective layer, a matt lacquer of
the type
57 0600/50 MHM can be used for example. If partial areas of the paper-of-value
surface are to be provided with a glossy protective lacquer layer, a suitable
gloss
lacquer for this purpose is a lacquer of the type 57 0199/50 MHM for example.
It is
preferable to use transparent and colorless lacquers, which do not change the
color of
the paper of value, for the protective lacquer layer, regardless of whether it
is
executed only as matt lacquer or also as gloss lacquer.
Soiling tests have shown that good results are achieved by applying a quantity
of about 2 to 15 grams per square meter of liquid, as yet uncured lacquer to
produce
the protective lacquer layer. The lacquer layer is preferably applied by
flexography
and screen printing. Flexography is an especially fast and economically
working
printing process that permits the transfer of sufficient quantities of
lacquer. Use of a
chamber doctor blade guarantees a reliable and troublefree production process.
In
flexography, about 2 to 8 grams of liquid lacquer per square meter of
substrate
surface is preferably transferred. Screen printing is preferably used for
applying
especially large quantities of lacquer in the range of about 5 to 15 grams per
square
meter.
Lacquering of the papers of value is done especially economically if it is
performed not on the individual paper of value but on a paper-of-value sheet
including a relatively large number of for example 24 to 60 individual papers
of
value. The protective lacquer can fundamentally also be applied to a
continuous
substrate web that is wound off a roll. Laminating a protective foil is
usually likewise
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done in a continuous process by which the paper of value and protective foil
are taken
off a roll. If the security elements are spaced-apart individual elements, the
foil can
contain the omitted areas as likewise spaced-apart holes. During lamination,
the areas
of the security elements are brought together in exact register with the
holes. If the
security elements are strip- or band-shaped, they extend over the total paper
of value
and thus along the total substrate web. In this case, the protective foil can
be
laminated on in sheetlike strips having no holes. Two adjacent foil strips are
laminated on at a distance apart so that the area for the security element is
left out.
For the protective lacquer one preferably uses aqueous dispersion lacquers,
which are not only relatively inexpensive but also uncritical from the point
of view of
industrial safety and environmental protection and can be handled and
processed with
little effort. Dispersion lacquers are particularly suitable for producing
matt surfaces.
However, radiation-curing lacquer systems, which crosslink under the influence
of ultraviolet (UV) radiation for example, are preferably used if large dry
layer
thicknesses are desired. Radiation-curing lacquers are also advantageous if
especially
high gloss is to be achieved. In an especially preferred embodiment, the main
portion
of the paper-of-value surface is covered with an aqueous dispersion lacquer to
produce a matt surface, while the partial area omitted in this lacquering,
where a
security element is located, is provided with a gloss lacquer that is
radiation-curing.
The successive lacquerings of the surface portions with matt or gloss lacquer
are
preferably effected in exact register, the partial area omitted in the matt
lacquering
being printed exactly with gloss lacquer. If exactly registered execution is
impossible
for reasons of production engineering, the execution is overlapping, whereby
the
permitted overlap zone is preferably no greater than about 2 millimeters.
The matt and glossy areas of the protective layer are clearly distinguishable
visually in the inventive paper of value due to their different gloss. What is
crucial is
not the absolute gloss value of the particular area, however, but the relative
difference
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between them. For checking by measurement technology, the surface to be
measured
can be illuminated at a defined angle and the reflected light measured
photoelectrically. If measurement is done for example using a reflectometer at
an
angle of 60 according to DIN 67530, or ISO 2813, ASTM D523 and BS 3900 Part
D5, the measured gloss units are preferably between about 5 and 10 gloss units
for
matt areas and preferably between about 15 and 35 gloss units for glossy
areas. The
difference between matt and glossy areas is preferably more than 10 gloss
units to
permit them to be well distinguished visually.
The inventive papers of value are furthermore testable without trouble by
means
of optical sensors in machine testing, since a clearly predominant portion of
the
paper-of-value surface is covered with a matt lacquer or matt protective foil
and thus
reflectionless. Since the omitted partial area of the paper of value
optionally covered
with gloss lacquer constitutes only a small fraction of its total surface,
optical sensors
can be aligned without problems in machine paper-of-value testing so that
their
detection area does not include the partial area omitted in the matt
lacquering or from
the matt protective foil.
According to a preferred example of the invention, a document has a print of
metallic effect ink as a security element, as mentioned above. The
surroundings of
said security element are lacquered with a water-base flexographic or screen
printing
lacquer as matt lacquer, and an oleographic lacquer applied to the security
element as
gloss lacquer. This avoids chemical decomposition of the metallic component of
the
metallic effect ink and a resulting clouding of the metallic luster. In this
variant it is
also possible to apply the oleographic lacquer to the security element and
then apply
the water-base matt lacquer all over, that is, also over the security element.
The
previously applied oleographic lacquer prevents the water-base lacquer from
being
accepted in the area of the security element.
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According to a further preferred embodiment of the invention, the area of the
paper of value where a security element is to be applied is additionally
pretreated to
achieve an optimal execution and/or optical effect of the security element.
Said
pretreatment can consist for example of applying a suitable background. If the
security element has for example a fine line print with line widths in a range
of about
50 microns and more, a higher resolution and sharper contours are obtained in
particular on rough substrate surfaces if the background is smoothed for
example by
an additional partial print. Instead of a print, the background for the
security element
can also be pretreated by coating part of the surface of a paper web with
suitable
coating mixtures. Special pretreatment of the background is also of advantage
for
blind embossings that are to render fine and extremely fine structures in the
range of
for example 100 microns and less. A plastically deformable coating, for
example of
polymers, partially applied prior to embossing results not only in better and
more
brilliant rendition of the fine structures but also stabilizes them
permanently.
While the invention has been described with reference to exemplary
embodiments, it will be understood by those skilled in the art that various
changes
may be made and equivalents may be substituted for elements thereof without
departing from the scope of the invention. In addition, many modifications may
be
made to adapt a particular situation or material to the teachings of the
invention
without departing from the essential scope thereof. Therefore, it is intended
that the
invention not be limited to the particular embodiment disclosed for carrying
out this
invention, but that the invention will include all embodiments falling within
the scope
of the appended claims, including equivalents to elements described therein.
