Note: Descriptions are shown in the official language in which they were submitted.
CA 02591982 2007-06-21
WO 2006/066431 PCT/CH2005/000754
DESCRIPTION
TITLE
Multilayer structure as a printing substrate and method
for the production thereof
TECHNICAL FIELD
A description is given of a multilayer substrate and a
method for the production of such a multilayer
substrate, which in particular can be used as a print
carrier, e.g. as a security document. The multilayer
substrate comprises at least one first paper layer, at
least one second paper layer and at least one plastics
layer of at least one thermoplastic polymer material
arranged between the paper layers and joined to the
paper layers. The flat substrate proposed can be used
for example as a print carrier, in particular as a
security paper, but also as a packaging material,
covering material, card substrate, etc.
PRIOR ART
Printing substrates for documents of value, such as
banknotes, are subjected to continuous further
development, in order to be able to meet the likewise
continuously growing requirements for security against
forgery. It is of particular interest to create
safeguards which, in daily use, can be detected by the
user without further technical aids but cannot readily
be imitated in terms of their nature. Such a feature
is, for example, the multitone watermark, such as is
traditionally used in security papers and is
established as a standard.
In the continuous striving for further-developed
substrates for banknotes, in addition to the known
CA 02591982 2007-06-21
WO 2006/066431 - 2 - PCT/CH2005/000754
security papers, alternative materials have also come
into use as a carrier material. For example, in
Australia since 1988, banknotes have been introduced in
which a polymer film is used as the printing substrate.
As compared with classic paper-based banknotes, such
polymer banknotes have diverse advantages, such as a
higher resistance to tearing or a higher resistance to
soiling. However, polymer banknotes have certain
important disadvantages in relation to security against
forgery as compared with banknotes made of security
papers. In particular, it is not possible to introduce
true watermarks in these substrates. In addition,
other established features used in paper substrates and
recognized by the consumer, such as mottled fibers,
planchettes or security threads, cannot be implemented
in polymer banknotes. Likewise, the characteristic
handle and sound typical of paper banknotes is missing,
which are often used as a clear recognition criterion
for authentic banknotes. The importance of the tactile
nature in distinguishing authentic and counterfeit
banknotes has been investigated, for example by the
Bank of Canada, and explained in SPIE Vol. 5310,
Optical Security and Counterfeit Deterrence Techniques
V, Analysis of Counterfeits and Public Survey Results
as Design Input, p. 63 ff.
In order to combine the advantages of the two banknote
substrates, combinations of the two materials have
already been proposed. For instance, EP 0 628 408
describes a substrate which consists of a printed film,
onto which a security paper is laminated on both sides
with the aid of an adhesive. The purpose of such
inventions is in each case, inter alia, to be able to
integrate additional security features, in particular
as print, between the two layers and to join two paper
layers.
CA 02591982 2007-06-21
WO 2006/066431 - 3 - PCT/CH2005/000754
In WO 2004/028825, a structure is proposed in which a
security paper is provided with a film on the surface.
In one possible embodiment, a paper web pierced in the
manner of a window is provided between two films. The
purpose of this invention is to protect the paper
surface on both sides in this way against soiling.
In addition to the improved durability mentioned, as
compared with conventional paper banknotes, polymer
banknotes have the possibility of additional
safeguarding against imitations which cannot be
implemented with classic paper substrates. If the
originally transparent polymer substrate is not printed
or printed only partially deliberately in certain
regions, the result is transparent regions, what are
known as windows, which are viewed as a valuable
safeguard against relatively simple and widespread
reproduction methods. These viewing windows are
classified as first-stage features, as they are known,
which, by definition, can be verified by the user
without the aid of additional apparatus. Since the
checking of the viewing window can be performed in a
particularly discreet way and, consequently, even
unconsciously, this feature is estimated by many
central banks to be extremely effective in principle.
In addition, with transparent regions, the possibility
is opened up of applying novel types of security
features which, in terms of their function, rely on a
transparent carrier material.
However, the substrate with which banknotes having such
viewing windows are implemented in the known cases has
important disadvantages in relation to security. The
characteristic handle and sound of a paper-based
banknote, often the most important characteristic when
detecting counterfeit notes, are entirely missing and
cannot be put back.
CA 02591982 2007-06-21
WO 2006/066431 - 4 - PCT/CH2005/000754
The treasured watermark, also known by the user and
still extremely secure, likewise cannot be implemented
in polymer substrates and can be put back only
unsatisfactorily by printing methods, a controversial
procedure since watermarks imitated by printing usually
expose a banknote as a forgery. Further security
features, likewise known in the public domain, such as
security threads and mottled fibers, likewise cannot be
implemented in polymer substrates or in any case put
back by printing methods in a manner which is
unsatisfactory and, as mentioned above, dubious.
It is to be viewed as a further disadvantage of the
polymer banknotes that these cannot be folded in the
usual way, since they spring back spontaneously. In
the event of a more insistent attempt to fold a polymer
banknote, a fold is achieved which no longer re-forms.
In the region of the folded edge, the printing is
typically lost; likewise the printing ink is worn away
quickly by use in a manner which is unusual for
banknotes. It is to be viewed as a further
disadvantage that, in the known cases, the polymer
substrate is an axially oriented polypropylene, a
material which is used in a similar quality in
innumerable products in everyday use, such as packaging
films, transparent films, sealing films, etc. and, as a
result, is available to a potential forger in a simple
way for imitations. The fact that the substrate used
is an axially oriented film proves to be
disadvantageous in particular when the substrate is
subjected to elevated temperatures, as can entirely
possibly occur in daily use, however. In the vicinity
of a hot hotplate or else under a halogen lamp, it is
entirely possible for such a polymer banknote to
shrivel up.
For all these reasons, banknotes on polymer substrate
have previously not gained any great significance and,
CA 02591982 2007-06-21
WO 2006/066431 - 5 - PCT/CH2005/000754
to some extent, after introduction has been carried
out, have even been replaced again by classic banknotes
based on paper substrate.
In the attempt, without the disadvantages mentioned,
nevertheless to implement the viewing window which is
treasured and classified highly as a security feature,
diverse attempts have been made to obtain such a
viewing window in a paper substrate as well.
For instance, DE 43 34 848 describes a paper carrier
having a window-like aperture which is closed with a
transparent covering film.
Another approach is described in WO 03/085193. There,
a security strip is incorporated into a security paper
in the paper forming process in such a way that viewing
sections are formed in the document of value. What is
common to both approaches is that the viewing window
can be implemented only in a defined strip region,
which results from the process from the supply of
covering film or security strip in the running
direction. In these regions, the substrate differs in
thickness and mechanical properties from the remaining
regions, which can have a disruptive effect both during
processing and in use.
Accordingly, WO 2004/076198 follows another approach
again, describing a multilayer laminate comprising
paper layers and film layers, in which the paper layers
in one preferred embodiment have fully penetrating
cutouts, which result in the desired viewing windows in
the laminate. The advantage of such a layer structure
lies in the fact that the viewing windows can be
implemented at any desired locations and in any desired
number in the document. The paper layers and film are
joined in a lamination process, in which any type of
adhesive is explicitly omitted. This proposal is a
CA 02591982 2007-06-21
WO 2006/066431 - 6 - PCT/CH2005/000754
technologically elegant approach but which, under
certain circumstances, involves certain economic and
process engineering difficulties. In particular, the
heating of the paper layers above the softening
temperature of the polymer film, which is inevitable
because of the process, is under certain circumstances
disadvantageous for the properties of the product. In
this process, the paper layers are highly dehumidified,
tend to yellowing or even to parchmentizing, which can
have detrimental effects on the optical properties
(shade, opacity) and the mechanical properties
(embrittlement, double fold number). It is to be
viewed as a further disadvantage of the process that,
in the case of apertures in the two paper layers, in
which the polymer film is freely accessible from one or
both sides, and thus a viewing window is formed which
is either covered on one side or else is fully
transparent, the polymer film is heated to the same
temperature as the remaining composite. At this
temperature, as a rule an increased ability of the
polymer to flow is provided, so that adequate
penetration into the paper layers occurs, forming a
penetration zone. Under these conditions, the polymer,
by its nature, likewise has an increased affinity with
the parts of the apparatus (rolls, carrier tapes) of
the laminator, which are at the same or even at a
higher temperature than that of the polymer, which can
lead to the polymer film sticking to the parts of the
apparatus and to the formation of some surface
structures.
SUMMARY OF THE INVENTION
Accordingly, the invention is based on the object of
providing a print carrier that is improved in
comparison with the prior art, in particular for use as
a security paper, and also a process for the production
thereof. In concrete terms, it concerns the provision
CA 02591982 2007-06-21
WO 2006/066431 - 7 - PCT/CH2005/000754
of a multilayer substrate and a method for the
production thereof, the multilayer substrate comprising
at least one first paper layer, at least one second
paper layer and at least one plastics layer of at least
one thermoplastic polymer material arranged between the
paper layers and joined to the paper layers. It
preferably concerns the provision of a multilayer
substrate and a method for the production thereof, the
multilayer substrate comprising at least one first
paper layer, at least one second paper layer and at
least one plastics layer of at least one thermoplastic
polymer material arranged between the paper layers and
joined to the paper layers, at least one of the paper
layers having fully penetrating apertures, which are
covered to their full extent by the plastics layer.
This object is achieved in that the plastics layer is
fed in between the paper layers in the molten state,
and the paper layers are then pressed between a pair of
rolls in a continuous process, the result being a
cohesive connection between the paper layers and the
plastics layer, forming a penetration zone in which
parts of the plastics layer are joined to the mass of
the fiber composite of the paper layers, and the
plastics layer having a weight per unit area of more
than 20 g/m2 and at most 100 g/m2.
The nub of the invention is thus to introduce a
plastics layer between two paper layers in such a way
that an intimate connection can be produced between the
paper layers without using adhesives in the process,
since the latter are frequently disadvantageous in
relation to security (adhesively bonded laminates can
be separated at the adhesive layers) Furthermore, at
the same time the plastics layer is to perform a
stabilizing and supporting function, which means that
the plastics layer not only serves as an adhesion
promoter between the two paper layers but reinforces
CA 02591982 2007-06-21
WO 2006/066431 - 8 - PCT/CH2005/000754
the multilayer substrate as a whole. This means that,
for example, the double fold numbers are increased to
an extreme extent as compared with pure paper
substrates, and thus a multilayer substrate is provided
which is substantially more durable, even with
intensive use. This is made possible by a thickness of
the plastics layer of more than 20 g/m2. In order
nevertheless to have paper-like tactile
characteristics, the plastics layer should be no
thicker than 100 g/m2.
From a completely different field, it is known that
multilayer laminates of paper with inner polymer layer
can also be obtained by the polymer being put in
between two paper layers in molten form in an extrusion
coating method. Such a solution is described, for
example, in US 2002/0176973 Al. In this text from
another technical field, a laminate having improved
dimensional stability under fluctuating atmospheric
humidity is described which comprises two layers of
paper with an inner layer of polymer, but the polymer
layer in each case is thicker than each of the two
paper layers.
Since this example originates from another technical
field, the product characteristics are also
substantially different from the characteristics which
are sought in the subject of the invention. For
example, no security papers, in particular no
watermarked papers, are used, which differ quite
substantially in terms of their strength and in their
optical and tactile characteristics from the kraft
papers and tissue papers used in US 2002/0176973 Al.
Furthermore, the preferred polymers of US 2002/0176973
Al are polyolefins which, on account of their
hydrophobic character, have a low affinity with paper.
Accordingly, the polymer does not penetrate into the
paper layers either (cf. US 2002/0176973 Al section
CA 02591982 2007-06-21
WO 2006/066431 - 9 - PCT/CH2005/000754
0040 and fig. 1/fig. 2), that is to say penetration
zones in the sense of the present invention are without
doubt not formed in US 2002/0176973 Al. The formation
of a penetration zone in which the polymer penetrates
at least partly into the fiber composite of the paper
layers is, however, an essential feature of the present
invention and of importance precisely for security
applications. This is achieved, inter alia, by
controlling the temperature of the laminator rolls
which, in contrast, in the case of the document from
the prior art US 2002/0176973 Al, are cooled to
temperatures of 15-30 C (cf. US 2002/0176973 Al,
section 0046).
As opposed to the present invention, which seeks a
multilayer substrate which differs little from
conventional security paper in its tactile
characteristics, in US 2002/01796973 Al, according to
the invention, a composite is achieved which, on
account of the relatively thick interlayer of polymer,
is stiffer and stronger than a conventional paper of
the same thickness.
According to a first preferred embodiment, the plastics
layer has a weight per unit area of 25-80 g/m2. A
weight per unit area of 25-40 g/m2 is quite particularly
preferred. In particular, the latter range proves to
be extremely advantageous since, firstly, a sufficient
supporting and stabilizing function of the plastics
layer is ensured and, at the same time, for example
when two identical paper layers with a thickness of
20-50 g/mz are used, a tactile behavior is achieved
which barely differs from a normal paper having a
corresponding total weight per unit area in the range
from 70-120 g/m2.
According to a further preferred embodiment, at least
one paper layer, preferably both paper layers, can on
CA 02591982 2007-06-21
WO 2006/066431 - 10 - PCT/CH2005/000754
average become as thick as or preferably thicker than
the plastics layer. In this way, inter alia, tactile
characteristics can be ensured which are similar to a
paper substrate, for example a security paper.
A further preferred embodiment is characterized in that
what are known as windows or at least regions in which
the plastics layer is exposed are provided. To this
end, at least one of the paper layers has at least one
cutout that is fully penetrating in some regions.
Correct windows can be formed by both paper layers each
having fully penetrating cutouts, and these cutouts
being supplied in a registered manner such that, at
least in some regions, viewing windows are formed, the
viewing windows preferably being at least translucent
or in particular preferably completely transparent. It
is also additionally or simultaneously possible for
both paper layers each to have fully penetrating
cutouts, and for these cutouts to be supplied in a
registered manner such that, at least in some regions,
regions are formed in which the plastics layer is
exposed only on one side. Here, too, at least in the
visible regions, the plastics layer is preferably
translucent or transparent.
The use of the weights per unit area specified above of
the paper layers and plastics layer thus permit, for
example, the production of stable and transparent
windows. However, it is also possible to provide
security features or the like in such windows, and it
is not necessarily the case that the windows have to be
completely transparent. For instance, it is possible
to provide (fluorescent) dyes or the like in the
plastics layer. However, it is preferred for the
thermoplastic polymer material of the plastics layer to
be a transparent material.
CA 02591982 2007-06-21
WO 2006/066431 - 11 - PCT/CH2005/000754
In relation to the material of the plastics layer, for
example the following materials have proven to be
suitable: polyethylene (PE), polypropylene (PP),
polyvinyl chloride (PVC), soft PVC (PVC-P), polystyrene
(PS), polyester, co-polyester, polycarbonate (PC),
polymethyl methacrylate (PMMA), polyoxymethylene (POM),
polyethylene terephthalate (PET), polyether ether
ketone (PEEK), polyamide (PA).
In the case of the preferred polyamide, in particular
polyamide 6 (PA6) or polyamide 12 (PA12) are suitable,
amongst others amorphous forms being preferred.
Furthermore, mixtures (blends) of the aforementioned
polymers or co-polymers are possible. For instance,
amorphous co-polyamide, preferably based on PA12, is
preferred.
According to a further preferred embodiment, the
thermoplastic polymer material of the plastics layer
has a glass transition point Tg and/or melting point Tm
above 0 C, preferably above 40 C. With such materials,
it is possible, for example for the extrusion, to work
at a melt temperature in the range from 250-350 , this
temperature preferably being set at the outlet from the
die. It transpires that an extrusion at a viscosity in
the range from 50-1200 Pa s, in particular in a range
from 500-1000 Pa s, is advantageous.
The method can preferably be carried out at a process
speed of more than 70 m/min, in particular preferably
more than 100 m/min. In other words, substantially
higher production speeds are possible than can be
achieved in laminating methods.
In order to be able to set the penetration zones
optimally without any damage to the paper layers, it
proves to be advantageous to heat at least one paper
layer, preferably both paper layers, substantially
CA 02591982 2007-06-21
WO 2006/066431 - 12 - PCT/CH2005/000754
immediately before the supply of the plastics layer.
This is preferably done exclusively on the side of the
paper web facing the plastics layer. In this case, the
heating can be effected by means of hot air blowers
and/or infrared radiators and/or in a heating duct
and/or over a heating table and/or over one or more
heated (calender) rolls.
According to another preferred embodiment, a line
pressure of 0-500 N/cm, ideally of 250-450 N/cm, is
applied between the pair of rolls immediately after the
introduction of the plastic layer by the extrusion. In
this case, the pair of rolls is preferably kept at a
temperature above room temperature. However, the roll
temperature should also ideally not lie above the melt
temperature or, respectively, above the glass
transition point of the materials used for the plastics
layer. Accordingly, it proves to be advantageous to
control the temperature of the pair of rolls to a
temperature in the range from 50-100 C, preferably in
the range from 60-80 C. A temperature just below the
glass transition point Tg and/or the melting point Tm of
the materials used for the plastics layer is preferably
chosen. Under certain circumstances, it can prove to
be advantageous to choose a roll temperature above the
glass transition point of the materials used for the
plastics layer. In particular, amorphous materials
normally have a course of the melt viscosity which
drops steeply as the temperature falls, so that roll
temperatures above Tg may be necessary for adequate
penetration. For instance, for a fully amorphous co-
polyamide 12 with T. of 155 C, a roll temperature of
Tg-45 to Tg-25 (about 110-130 C) has proven to be
optimal, for a partially crystalline co-polyamide 12
with Tm of 178 C, a roll temperature of Tm-105 to Tm-90
(about 75-90 C). Depending on the material used, the
ideal roll temperatures may also be different, which,
if necessary, requires roll temperature control by
CA 02591982 2007-06-21
WO 2006/066431 - 13 - PCT/CH2005/000754
means of oil temperature control, by which means roll
temperatures up to 180 C can be achieved.
The method is preferably set in such a way that the
penetration zones have an average thickness in the
range from 5-30 pm, in particular preferably in the
range from 10-20 pm.
A surface which is particularly smooth and therefore
optimal in relation to transparency, in particular in
the windows, can be achieved by high-gloss polished
steel rolls being used as rolls. The rolls can
optionally be anti-adhesion finished, which promotes
the separation of the windows from the roll. For
instance, surfaces of PTFE, Teflon surfaces, surfaces
made of chromium or chromium steel with implanted
Teflon particles (also known under the trade name
TeFlok), silicone surfaces, surfaces of poly(imide),
etc., are suitable. Furthermore, it can prove to be
expedient if one or both rolls have a ductile surface.
As a result, a more homogeneous pressure distribution
can be achieved over the total width of the web. This
can be advantageous in particular if one or both paper
webs have fully penetrating cutouts, in the region of
which, because of the lack of material, less pressure
can be applied via the rolls. Ductile rolls are able
to compensate for this pressure difference, which
results in improved adhesion in these regions as well.
Such rolls are, for example, rubber rolls coated with
PTFE or rubber rolls encased in PTFE or silicone-coated
rolls.
As already mentioned further above, security features
or combinations of security features can be
incorporated in the plastics layer. In this case, for
example the following are possible: mottled fibers,
planchettes, metal fibers, marking materials, IR or UV
dyes, security pigments, fluorescent dyes, effect
CA 02591982 2007-06-21
WO 2006/066431 - 14 - PCT/CH2005/000754
pigments or security threads, these security features
being added to the polymer mixture or the melt as
additives or scattered in the vicinity of the roll nip
or blown onto the web of melt or, in the case of the
security thread, led into the roll nip.
Likewise, it is preferably possible to provide security
features in the paper layers. In this case, such
security features can be arranged only in one paper
layer or, for example, different security features can
be used in the two paper layers. Thus, the security
features already known from the region of papers as
substrate for banknotes can be used without further
modification. As security features of the paper
layers, for example the following can be used:
watermarks, in particular gray-stage watermarks,
security threads, OVD, mottled fibers, security
pigments, iridescent ink applications, chips, in
particular RFID chips, magnetic strips.
In particular when windows are to be produced and these
are to have as homogeneous a surface as possible,
according to a further embodiment, the molten polymer
layer can be put in via a die which is in immediate
contact with the paper layers. Alternatively or
additionally, it is possible to ensure that the molten
polymer layer is put in via an engraved roll, a screen
printing roll or an applicator roll, in particular by
using a three-roll unit.
It is preferred to form the plastics layer over
substantially the entire area of the two paper layers.
However, it is also possible to arrange a plastics
layer only in some regions or in stripes and/or to
configure the plastics layer to have a different
thickness in some regions or in stripes.
CA 02591982 2007-06-21
WO 2006/066431 - 15 - PCT/CH2005/000754
The extrusion can be carried out on the basis of a
simple melt but, alternatively, it is also possible to
use for the material of the plastics layer a pre-
polymer, a polymer dispersion or a polymer solution
which, during or following the connection to the paper
layers, cures chemically or physically and/or reacts
and/or dries and/or gels.
Furthermore, the present invention relates to a
multilayer substrate as can be produced in a method
described above or, respectively, as is actually
produced by a method as described above.
Such a multilayer substrate is preferably characterized
in that at least one of the paper layers has at least
one fully penetrating cutout in some regions, these
preferably two paper layers each having fully
penetrating cutouts and these cutouts being supplied in
a registered manner in such a way that viewing windows
are formed, at least in some regions, and that in the
edge region of the cutouts there are flattened
portions, which means that transitions from paper to
polymer have a lower edge height than the paper
thickness (cf. also fig. 3).
In a preferred variant of this embodiment, the combined
cutouts of the two paper layers differ from one another
in shape and/or size, so that the result is a viewing
window which is characterized by an edge region which
is covered by a paper layer only on one side. Such an
embodiment is preferred for reasons of security against
forgery, since it makes the multilayer structure
visible, which cannot be put back by using a single
paper layer.
A particularly preferred embodiment is characterized in
that both paper layers in each case have fully
penetrating cutouts, and these cutouts are supplied in
CA 02591982 2007-06-21
WO 2006/066431 - 16 - PCT/CH2005/000754
a registered manner in such a way that, at least in
some regions, viewing windows and/or regions are formed
in which the plastics layer is exposed only on one
side, the plastics layer having at least one security
feature in the form of a security thread, the security
thread being led into the roll nip, and the security
threads being visible in top view in the viewing
windows and/or regions in the final multilayer
substrate. The regions in which the plastics layer is
exposed only on one side are in particular preferably
arranged in a registered manner alternately on the top
side and underside of the multilayer substrate
preferably in the direction in which the security
thread runs, in such a way that the security thread is
visible from both sides in top view as a window thread.
Such a multilayer substrate exhibits substantially
increased security against forgery, in particular in
combination with specific security threads which, for
example, have fluorescent and/or polarizing and/or
conductive features.
As already mentioned further above, the thermoplastic
polymer material of the plastics layer is in particular
a transparent material and, in regions of viewing
windows, these are highly transparent and have a smooth
surface. The material of the plastics layer is a
polyamide, preferably an amorphous polyamide,
preferably having a glass transition point above 20 C;
preferred in particular is a polyamide 12 and/or an
amorphous co-polyamide 12. The paper layers have a
weight per unit area in the range from 5-500 g/m2,
preferably in the range from 10-80 g/m2, in particular
preferably in the range from 20-40 g/m2. According to
a preferred embodiment, at least one paper layer is a
security paper. According to a further preferred
embodiment, at least one paper layer has a watermark.
The papers can have been made, for example, on a
CA 02591982 2007-06-21
WO 2006/066431 - 17 - PCT/CH2005/000754
cylinder paper machine or on a fourdrinier paper
machine.
According to a preferred embodiment, the multilayer
substrate has a double fold number which is
substantially higher than that of normal paper
carriers, which means that it has a double fold number
of more than 1800, in particular of more than 5000.
Furthermore, the present invention relates to the use
of such a multilayer substrate as a covering material,
packaging material, card material, security paper, in
particular as a banknote, check, ticket, certificate,
share document, bond document, deed, identity document,
access document.
Further preferred embodiments of the method, of the
multilayer substrate and of its use are described in
the dependent claims.
BRIEF DESCRIPTION OF THE FIGURES
The invention is to be explained in more detail below
by using exemplary embodiments in conjunction with the
drawings, in which:
fig. 1 shows the schematic process for the production
of a multilayer composite according to the
invention by putting in a melt by means of
extrusion; and
fig. 2 shows a cross section through a multilayer
substrate produced in this way.
Fig. 3 shows a micrograph of a cross section through a
multilayer composite according to the invention
with a semitransparent window (covered by paper
on one side).
CA 02591982 2007-06-21
WO 2006/066431 - 18 - PCT/CH2005/000754
Fig. 4 shows a schematic drawing of a complete system
for the production of a multilayer composite
according to the invention.
WAYS OF IMPLEMENTING THE INVENTION
The subject of the present invention is to solve the
aforementioned disadvantages in the production of a
multilayer laminate and the aforementioned
disadvantages of the product characteristics resulting
therefrom by using plastic films, in that a laminating
process, as proposed in WO 2004/076198, for example, is
omitted and, instead, a multilayer substrate 60 based
on a first paper layer 10 and a second paper layer 20
and polymer 80 is produced in such a way that the
polymer is put in as a polymer melt 30 already in
molten form.
Accordingly, the present invention relates to a process
in which technologies from flat film extrusion are
transferred to a coating application, which means that
for the first time a multilayer composite can be
produced which consists of paper layers (at least one
thereof made of security paper) which, for example,
have fully penetrating apertures, which are covered
over completely with a film-like polymer layer without
the use of a prefabricated film.
In this way, as compared with the laminating variants
known in the prior art, the costly preforming of a flat
film is dispensed with, just like the melting of the
film in direct contact with the paper webs, which is
cumbersome, time-consuming and damaging to the paper.
Instead, as illustrated in figure 1, polymer granules
are melted and conveyed in an extruder and, through a
fishtail die 40, are extruded directly in the molten
phase as a polymer melt 30 onto or between the paper
layers, for example supplied from a roll. The term the
CA 02591982 2007-06-21
WO 2006/066431 - 19 - PCT/CH2005/000754
molten phase in this connection means a state of the
polymers which is characterized by an increased
deformability and a reduced viscosity. In this case,
the viscosity lies in a range between 20 and 2000 Pa s
which is suitable for polymer processing, in particular
the production of flat films, preferably in the range
from 50 to 1000 Pa s, in particular between 75 and
500 Pa s. In this case, it is unimportant whether the
polymer melt is a polymer with a defined melting point
Tm or defined melting interval Tm 4T at a temperature
above the melting temperature Tm or whether this is a
polymer without a defined melting point, which is
present in a form heated so far above the glass
transition point Tg that the viscosity of the material
is reduced to such an extent that processing in the
manner proposed is possible. Polymers which fall into
the first class are, for example, partially crystalline
polymers such as polyethylene (PE), polypropylene (PP),
polyethylene terephthalate (PET), polyamide 6 (PA6),
polyamide 12 (PA12), partially crystalline co-
polyamides and partially crystalline co-polyesters.
Polymers which fall into the second class are, for
example, amorphous polymers such as polyvinyl chloride
(PVC), polystyrene (PS), polycarbonate (PC), polymethyl
methacrylate (PMMA) or else amorphous co-polyamides
(e.g. based on PA12) and amorphous co-polyesters, such
as are produced by Ems (EMS Chemie, Domat-Ems,
Switzerland), for example.
Some examples of polymers with and without defined
melting points which are particularly suitable for the
application are given in the following table 1.
Table 1
Polymer Tg T.
Polyethylene (PE) -110 to -90 C 135 C
Polypropylene (PP) -10 C 175 C
CA 02591982 2007-06-21
WO 2006/066431 - 20 - PCT/CH2005/000754
Polyvinyl chloride (PVC) 50 to 90 C -
Polystyrene (PS) 100 C -
Polycarbonate (PC) 150 C -
Polymethylmethacrylate (PMMA) 105 C -
Polyoxymethylene (POM) 125 C 175 C
Polyethylene terephthalate (PET) 70 C 265 C
Polyether ether ketone (PEEK) 145 C 335 C
Polyamide 6 (PA6) 50 C 215 C
Polyamide 12 (PA12) 45 C 178 C
Partially crystalline
co-polyamide L25, Ems 45 C 178 C
Partially crystalline
co-polyamide L16, Ems 50 C 178 C
Amorphous co-polyamide G21, Ems 125 C -
Amorphous co-polyamide TR90, Ems 155 C -
Preferred materials for carrying out the aforementioned
application are, in particular, polymers from the class
of polyamides. On account of their chemical structure,
these have a particularly high affinity with paper.
The reason for this fact is the formation of hydrogen
bridges between the amide groups of the polyamide and
the polar groups of the cellulose fibers of the paper.
A multilayer substrate made of these preferred
materials with paper is therefore distinguished by a
particularly intimate bond, which is based firstly on
good cohesion and secondly on good compatibility of the
individual components. The intimate cohesion may
possibly be a consequence of good wettability of the
paper fibers with the polymer melt used. A further
polymer class which is distinguished by good
wettability and likewise results in composites with
intimate cohesion is the polyesters. If appropriate,
adequate cohesion can also be achieved with polymers
which do not have the aforementioned possibility of
forming hydrogen bridges, for example with polyolefins
such as polyethylene or polypropylene.
CA 02591982 2007-06-21
WO 2006/066431 - 21 - PCT/CH2005/000754
Further advantageous properties of a polymer material
for a substrate according to the invention are high
chemical resistance to acids, bases, solvents,
bleaching agents etc, high thermal resistance, high UV
resistance, high transparency, high cyclic bending
strength, high softening temperature. From this point
of view, polyamides are particularly well suited, for
example polyamide PA12 or co-polyamides based thereon.
Since the polymer in the sense of the invention strikes
the paper directly in molten form, the influence of
heat on the paper occurs briefly and therefore in a
barely damaging manner. It is possible to operate with
comparatively high melting temperatures in the range
from 300-350 C which, in the case of a laminating
process, could not be applied or could be applied only
with generally irreversible damage to the paper. This
has the advantage that, as a result of the high
temperature of the melt, a lower melt viscosity can be
achieved, which permits easier and faster penetration
into the paper and an intimate bond required for a
security substrate. At the same time, higher process
speeds are permitted. Extrusion coating systems can
accordingly also be operated without problems at
process speeds of up to 500 m/min, while belt presses
for the lamination when using plastic films are
normally not operated at more than about 50 m/min. In
the case in which a belt press or a roll laminator is
used for the production of a multilayer substrate with
a polymer film, the working temperature is restricted
to about 200 C, since otherwise the paper is
irreversibly damaged. At these temperatures, no
adequate connection to the preferred materials, as is
required for such a product, can be achieved. When an
extrusion coating system is used, the required
connection of the same materials is made possible,
however, since the hot, free-flowing melt is able to
penetrate sufficiently deeply into the paper surface
CA 02591982 2007-06-21
WO 2006/066431 - 22 - PCT/CH2005/000754
without the latter having to be brought to a
temperature damaging to the paper.
The melt viscosity at a given temperature also depends
in an indirect way on the shear rate, which offers a
further possibility for setting the processing
parameters and which makes the process management
easier, in particular at elevated production speeds.
A further advantage of the method proposed is that, in
a composite produced in this way, substantially lower
layer thicknesses of polymer can be achieved than would
be possible by means of lamination with a polymer film.
The fact that, in the method according to the
invention, the polymer in molten form is picked up
directly by at least one supporting paper means that
substantially thinner but still loadbearing and
supporting layers can be achieved. This applies in
particular to a multilayer input of polymer, which can
be applied from one and the same fishtail die by using
a plurality of extruders and an appropriate multilayer
tool. Appropriate apparatus from extrusion technology
can be adopted, in particular from the flat film
extrusion sector.
A further advantage of the extrusion process according
to the invention resides in the flexibility in relation
to the variation of the polymer to be processed.
Material changes are possible within an extremely short
time, which also makes the production of smaller batch
sizes attractive. In addition, marking substances,
dyes, security pigments, fluorescent dyes, effect
pigments, interference pigments, metal pigments,
reactive dyes, UV absorbers, stabilizers and further
additives, preferably in the form of a master batch,
can be metered into the polymer granules in a simple
way before extrusion, which permits simple
CA 02591982 2007-06-21
WO 2006/066431 - 23 - PCT/CH2005/000754
individualization and further safeguarding of the
product.
A central difficulty in the production of the desired
product resides in the formation of transparent, even
windows. Substrates which are laminated with polymer
on extrusion coating systems normally have no fully
penetrating apertures. Accordingly, the documents
known from the prior art also do not have any paper
webs which have apertures in which viewing windows
covered with polymer would be formed in the extrusion
coating process. Extrusion coating systems for the
production of paper composites are normally constructed
in such a way that the paper is laid on a roughened,
temperature-controlled or cooled steel roll, a second
paper web led over a press roll covered with rubber is
pressed against the first steel roll, and the polymer
melt is extruded into the roll nip produced. This is
in particular also the case in the document US
20020176973 Al mentioned further above, where roll
materials made of rubber or other materials with a
ductility of rubber are explicitly used. Experience
shows that such a configuration does not permit the
formation of transparent, even windows in the region of
cutouts in the paper webs. The roughened surface of
the temperature-controlled steel roll is transferred
into the molten polymer which, on the opposite side,
adheres strongly to the rubber press roll. Cooling of
the temperature-controlled pair of rolls far below the
solidification temperature of the polymer may reduce
the adhesion to the rubber roll somewhat but,
nevertheless, a certain amount of bulging of the
windows cannot be avoided; it is equally barely
possible to achieve a smooth surface needed for
adequate transparency.
The subject of the invention is then, inter alia, to
choose a structure in which two high-gloss polished
CA 02591982 2007-06-21
WO 2006/066431 - 24 - PCT/CH2005/000754
steel rolls whose temperature can be controlled are
chosen as the pair of rolls 50. Such a configuration
is unknown for a thin, less voluminous composite as in
the present case. Extrusion coating systems which
operate with two steel rolls (instead of one steel roll
and one rubber roll) are, however, used for processing
voluminous, thick materials such as spun bonded
nonwovens. The choice of two high-gloss polished steel
rolls, which is unusual for the production of a thin,
paper-based composite, now permits the formation of
mirror-smooth, even, highly transparent viewing windows
with the quality of an extruded flat film.
The cooling of the melt in contact with the rolls is
largely carried out sufficiently quickly to prevent
possible crystallization of the polymer. The roll
temperature, as opposed to the roll temperature in a
laminator, is chosen to be lower than the softening
temperature of the polymer, which largely prevents the
polymer adhering to the roll. Nevertheless, at the
interface between polymer and paper, an adequately
intimate bond is brought about by the formation of a
penetration zone, in which the polymer at least partly
encloses the fiber composite of the paper. One
supposed reason for this is a certain insulating action
of the paper, which has a low thermal conductivity. In
contact with the paper web, the polymer melt therefore
cools slowly, so that it is able to penetrate
sufficiently deeply into the paper surface until it
solidifies. Here, it proves to be advantageous that
the penetrating melt comes closer to the cooler roll
surface as the penetration depth increases, and thus
the dissipation of heat takes place more quickly and
the melt consequently solidifies more quickly the more
deeply it penetrates into the paper. This self-
regulating mechanism can be used to set the penetration
depth of the polymer exactly and to prevent complete
penetration of the polymer as far as the paper surface.
CA 02591982 2007-06-21
WO 2006/066431 - 25 - PCT/CH2005/000754
As opposed to this, in the laminating process in a hot-
press or a roll laminator, the highest temperatures are
to be met on the laminate outer side, so that the
polymer film becomes more free-flowing the more deeply
it penetrates into the paper layer. On the other hand,
the lowest temperatures are to be met in the core of
the laminate, where the joining of polymer and paper is
intended to occur. A product produced in this way
firstly tends to exhibit points on the surface through
which polymer has penetrated completely and secondly to
exhibit poorer composite adhesion. These disadvantages
of the laminating variant described in the prior art
have a detrimental effect on a product which has
viewing windows. The polymer film in the exposed zones
experiences the highest temperatures in the laminating
process, since it comes to lie directly on the heated
parts of the apparatus and therefore becomes more free-
flowing than the polymer film located in the interior
of the paper composite. This leads firstly to the
surface structure of the parts of the apparatus being
molded onto the windows and secondly, separating these
free-flowing, sticky windows from the parts of the
apparatus is barely possible without deformation.
Consequently, the present invention is based, inter
alia, on the surprising finding that a polymer melt can
be extruded from a die directly into the nip between
two temperature-controlled rolls, on which in each
case, for example, a paper web provided with fully
penetrating cutouts 90 (cf. fig. 2) runs, and, as a
result, a multilayer composite can be achieved which
has both highly transparent viewing windows 100 and an
excellent connection of the individual layers to one
another as a result of the formation of a penetration
zone 120.
The pair of rolls 50 chosen in this case is preferably
two high-gloss polished steel rolls, and the
CA 02591982 2007-06-21
WO 2006/066431 - 26 - PCT/CH2005/000754
temperature of the pair of rolls is preferably set in
such a way that the polymer melt, in the regions where
the latter is in direct contact with the rolls, is
cooled sufficiently quickly to an adequately low
temperature, so that adhesion to the roll surface is
largely prevented;, secondly, in regions where the
polymer melt is in contact with the paper layers, the
polymer melt maintains an adequately low viscosity in
order to penetrate into the paper layers to a
sufficient extent, forming a penetration zone 120, in
order to permit an intimate bond.
Such a process presumably benefits from the fact that
the melt solidifies more quickly in the event of direct
contact with the temperature-controlled roll surface
than when said melt is separated from the roll surface
by a paper layer, which results in slower cooling as a
result of a certain insulating effect of the paper
layer. A roll temperature just below the softening
temperature of the polymer in contact with the roll is
preferably chosen, so that the polymer in direct
contact with the roll immediately solidifies to form a
sufficiently strong film but, in regions in which the
polymer is separated from the roll by the paper layer,
the polymer temperature still remains above the
softening temperature for a certain time, in order to
permit adequate penetration into the paper layer. In
this connection, it may prove advantageous to preheat
the paper before supplying the polymer melt. This can
be done, for example, by means of infrared radiant
heaters and also by means of hot air blowers.
Alternatively, the paper web can be drawn through a
heating duct or over a heating table for the purpose of
being heated, or wrapped around one or more heated
rolls, in particular heated calender rolls. The paper
surface located on the inside in the composite is
advantageously heated more intensely or brought to a
higher temperature than the side facing away from the
CA 02591982 2007-06-21
WO 2006/066431 - 27 - PCT/CH2005/000754
polymer layer. This is done, for example,
automatically when use is made of an infrared radiant
heater which is aimed at the paper surface located on
the inside in the composite.
Additionally or alternatively, the penetration of the
polymer melt into the paper surface and/or the polymer
adhesion can be promoted by the paper being pretreated.
Adhesion promoters which improve the wettability of the
paper with the polymer melt can prove to be
advantageous, as can primers which additionally react
with one or both components. Possible additives which
can be added in the body of the paper or via the size
pond in a size press, for example, or can be applied in
the coating process, are for example dispersions and/or
emulsions of polymers, in particular of amphiphilic
polymers. Other pretreatment agents, primers as they
are called, are known to those skilled in the art.
Such additives are offered, for example by Trub
Emulsions Chemie AG, Ramsen, Switzerland, explicitly
for the extrusion coating of paper. Furthermore, in
order to improve the adhesion, the papers can be
surface-activated with corona treatment, ozone
treatment, flame treatment and further methods known to
those skilled in the art.
The penetration of the polymer into the paper layers is
additionally simplified by the melt film being in
contact with the paper layer under increased pressure
as compared with the direct contact with the roll. For
these two reasons, adequately deep penetration of the
melt into the paper layer, and therefore the formation
of a penetration zone 120 necessary for an intimate
bond, is made possible even at high process speeds. A
further positive effect of the increased pressure in
the transition region of the fully penetrating aperture
90 is that a certain flattening 70 of the edge around
the aperture 90 is formed, which leads to a soft
CA 02591982 2007-06-21
WO 2006/066431 - 28 - PCT/CH2005/000754
transition between paper layers 10 and viewing window
100. As opposed to a sharp-edged transition, such as
would be produced for example in the case of lamination
of a paper layer having fully penetrating apertures
with a film with the aid of an adhesive, the risk of
inadvertent or else deliberate destruction of the bond
by attacking this edge is reduced dramatically.
When two paper layers provided with fully penetrating
apertures are used, the apertures preferably lie one
above the other, at least in some regions (registered
supply), in order to obtain completely transparent
viewing windows, at least in some regions. However,
the fully penetrating apertures do not necessarily need
to be identical and/or congruent. In a preferred
embodiment, at least one of the paper layers contains a
watermark 110.
A cross section through a substrate according to the
invention is shown in fig. 3 in a micrograph in a
section at right angles to the plane of the paper. In
this case, only one of the paper layers 10 is provided
with a cutout 90, so that a region 91 is formed in
which the polymer layer is exposed only on one side.
A system which produces a multilayer substrate
according to the invention, which comprises a first
layer of watermarked paper 214 having fully penetrating
cutouts coordinated with the watermarks, and a layer of
paper 202 having cutouts coordinated with the cutouts
of the first layer, and comprising a polymer layer
located on the inside, which is extruded in molten form
in between the two paper layers brought into congruence
and provided with fully penetrating cutouts, is shown
schematically in fig. 4. In this case, continuous
arrows designate material transport, dashed arrows
designate data flow.
CA 02591982 2007-06-21
WO 2006/066431 - 29 - PCT/CH2005/000754
The paper web 202 made of conventional paper is in this
case supplied from an unwind 201 and led first through
a draw controller 203 and a web edge controller 204.
The cutouts are then produced in a punching unit 205
and the punched-out portions are removed in an
extraction system 206.
For its part, the paper web 214 made of watermarked
paper is supplied via an unwind 212 and introduced into
the method via a web edge controller 204. After this
there is a watermark reader 213 and once more a
punching unit 205 for producing the cutouts in a manner
in register with the watermarks.
In parallel with this, the plastics layer or the
material to be used for this purpose is prepared by the
material being supplied from a dryer 207 and, if
appropriate, mixed with a further material, for example
a master batch from a metering device 208, and led via
an extruder 209 to a die 211.
The two paper webs 202/214 are firstly heated on the
side facing the plastics layer by an infrared radiant
heater 210 in each case, and then rolled into the nip
between the two rolls 50 with the simultaneous supply
of the plastic from the die 211. The multilayer
laminate produced in this way is then inspected in a
web inspection final control facility 215 and marked
with an inkjet marking system 216 that may be present,
and led over a web accumulator/cutting table 217 and
wound up at the end of the apparatus 218.
In a preferred form, a multilayer melt curtain
comprising various polymers is supplied as the molten
polymer. The structure of such a multilayer melt
curtain is preferably symmetrical, for example having
an inner layer of a first polymer and in each case an
outer layer of a second polymer. The softening
CA 02591982 2007-06-21
WO 2006/066431 - 30 - PCT/CH2005/000754
temperature of the outer polymer preferably lies below
that of the inner polymer or, respectively, the outer
polymer has a lower melt viscosity than the inner
polymer under the given processing conditions. In this
way, by means of a suitable choice of the outer
polymer, the bonding to the paper layers or the
chemical resistance can be optimized, while a material
for an optimized formation of the windows can be chosen
as the inner polymer layer. Preferably, such a
multilayer polymer layer can involve largely compatible
polymers, such as various types of polyamides or
various types of polyesters. However, multilayer
polymer layers of different, not necessarily
compatible, polymer classes can also be made, such as a
polymer layer having an inner core of a polyamide and
outer layers of polyolefins, for example polyethylene
or polypropylene.
It can generally prove to be advantageous to lead the
multilayer composite as tangentially as possible to the
roll nip over a certain distance following the input of
the polymer, or to lead it away from the curved roll
surfaces at least before complete cooling and to lead
it onward over a certain distance in a straight line,
that is to say not curved around a radius, in order to
permit the most complete solidification of the polymer
layer possible in the finally desired attitude of the
multilayer composite and to improve the planarity of
the substrate.
It is possible for additives, such as marking
substances, dyes, IR dyes, UV dyes, fluorescent dyes,
substances with an anti-Stokes shift, security
pigments, effect pigments, interference pigments, metal
pigments, etc. to be added to at least one layer of the
polymer layer possibly formed with multiple layers.
CA 02591982 2007-06-21
WO 2006/066431 - 31 - PCT/CH2005/000754
The polymer layer can also be formed thicker in some
regions. This is possible in a particularly
straightforward way with a segmented fishtail die, by
individual lip segments being opened somewhat more
widely. In this way, the possibility results of
increasing the quantity of the polymer applied, for
example in the region of the windows, in order to
obtain more stable windows. In addition, in the region
of the stripe in which a watermark is possibly located,
it can also prove to be advantageous to configure the
intermediate polymer layer somewhat thicker than in
adjacent regions, in order to compensate for the
thickness differences in the paper caused by the
watermark and at the same time to maintain the contrast
richness of the watermark. Furthermore, in this way a
tactile material can be achieved in a straightforward
manner, since the polymer layer that is thicker in some
regions consequently exhibits detectable thickening and
stiffening of the substrate in this region.
Furthermore, it can prove to be useful to form the
zones in which the edges of the security document
subsequently come to lie to be somewhat thicker, since
in particular these edges are susceptible to wear and
tearing, which can be influenced beneficially by an
increased input of polymer.
Furthermore, in the production process of a multilayer
substrate according to the invention, additional
material can also be incorporated between the layers.
For example, it is conceivable to arrange for a
security thread to run into the roll nip as well, which
in this way is also incorporated firmly between the
individual layers. Ideally, the thread is provided
with an adhesive, as is not unusual for security
threads, and is led over the temperature-controlled
roll in such a way that it is already bonded to one
paper layer by an adhesive bond, which means that the
risk of the thread tearing as it enters the polymer
CA 02591982 2007-06-21
WO 2006/066431 - 32 - PCT/CH2005/000754
melt is minimized. Surprisingly, security threads can
actually be processed at the same time by having them
run into the roll nip, specifically even in cases in
which the melting point of the thread material lies
below the melt temperature of the polymer melt as it
emerges from the die. It has been shown that, given a
sufficiently short contact time, which is provided at
the intended production speeds of more than 25 m/min,
the threads do not melt. For example, security threads
made of polyester and also security threads made of
monoaxially oriented polypropylene (MOPP) have been co-
processed successfully at speeds of 30 m/min and melt
temperatures at the die of 325 C.
In a preferred embodiment, the threads are introduced
over the window position in such a way that the thread
is visible in the window in the finished product. In
this case, the window can be a transparent window,
which has been produced from two apertures brought over
each other congruently, but can also be a
semitransparent window, which is covered on one side by
paper and which has been produced only from the
aperture of a single paper layer. In the first case,
the security thread is directly visible in the window
from both sides of the document; in the second case it
is directly visible only from one side of the document
and is visible from the opposite side only in
transmitted light. Of course, a plurality of windows
can be accommodated in a document; in the case of
semitransparent windows, the coverings can be located
both on one and on the other side of the composite. In
the last-named case, by using a security thread which
is led through a series of semitransparent windows in
which the transparent sides alternate, the result is
the possibility of obtaining a window thread in the
document which is visible in segments from one and from
the other side of the document. By contrast, the
papermaking methods of introducing a window thread only
CA 02591982 2007-06-21
WO 2006/066431 - 33 - PCT/CH2005/000754
permit the thread to be visible in segments from one
side but not from the other side of the document.
Furthermore, it is conceivable to print the paper
layers, for example in the inkjet process, on the
inside in the multilayer laminate, during or before the
processing process. In this way, a print is produced
which is hidden in the document, is ideally individual
and can be detected only when looked through and cannot
be forged from outside. Of course, other further
printing processes are also conceivable which apply a
non-individual or else likewise an individual print
that can be varied during the process. Alternatively
or additionally, the print can also be applied to the
outer paper surface. Offset printing units are
preferably used, which can be synchronized with the
punching units 205 in a straightforward manner.
Furthermore, during the processing process, it is
possible to scatter, spray on or blow on substances
such as mottled fibers, planchettes, pigments, dyes,
metal fibers, metal flocks, etc. in the vicinity of the
roll nip. This can be done both in the case of one and
in the case of both paper layers but, alternatively or
additionally, can also be done on the melt tail.
Furthermore, during the processing process, it is
possible to arrange to dispense objects onto the paper
web or to feed them in dispensed form onto a carrier,
for example tuned electronic circuits, transponders,
electronic chips, RFID chips, electrically conductive
structures, such as printed, etched or deposited coils
or antennas, metal platelets, magnetic particles, etc.
In a preferred process, the molten polymer layer is put
in via a melt curtain, which is extruded from a die
that is at a specific distance from the paper surface.
CA 02591982 2007-06-21
WO 2006/066431 - 34 - PCT/CH2005/000754
In an alternative production variant, the molten
polymer layer is put in via a die which is in direct
contact with the paper layer. In this way, ideally
complete filling with polymer of the fully penetrating
apertures in the paper layer can be achieved, while the
quantity applied on the remaining paper layer turns out
to be lower.
In a further production variant, the molten polymer
layer is put in via an applicator roll, for example by
using a three-roll unit, as is known from coating
technology. In an alternative production variant, the
molten polymer layer is put in via an engraved roll, as
is known from coating technology. In an alternative
production variant, the molten polymer layer is put in
via a screen printing roll, as is known from coating
technology.
The molten polymer layer can be interrupted, at least
in some regions.
The molten polymer layer can be a pre-polymer, a
polymer dispersion or a polymer solution which, during
or following the bonding to the paper layer, cures
chemically or physically and/or reacts and/or dries.
EXAMPLES
Example 1
In each case a paper with a weight per unit area of
g/m2 which had punched-out portions in some regions
was led over two temperature-controlled, high-gloss
polished steel rolls. The pair of rolls was moved
35 together, so that the two paper webs were in contact
with each other. A melt made of an amorphous polyamide
with a melt temperature of 300 C was poured into the
roll nip from a die. The input quantity was about
CA 02591982 2007-06-21
WO 2006/066431 - 35 - PCT/CH2005/000754
35 g/m2. The pair of rolls had a temperature of 75 C
and the process speed was 40 m/min. The result was a
multilayer composite which, in the regions of
overlapping punched-out portions in the paper, had
windows of polymer and which could not be separated
without destruction. The windows had excellent
transparency and a mirror-smooth surface. The process
speed could be raised to 70 m/min without changing the
quality of the composite and of the windows. The input
quantity could likewise be reduced to about 25 g/m2
without changing the quality of the composite and of
the windows. Stable, even windows were still obtained.
Comparative example to example 1
In a belt press, two paper layers of a weight per unit
area of 35 g/m2, which had punched-out portions in some
regions, were processed with a centrally located film
of about 35 pm thickness made of the same amorphous
polyamide as in example 1 to form a laminate. The
temperature of the belt press was 280 C, the heated
section had a length of about 1 m. After passing
through the heated section, the laminate was led in the
hot state through a pair of calender rolls with a line
pressure of 2100 N/cm and subsequently cooled. In
order to achieve adequate bonding, it was not possible
to exceed process speeds of 5 m/min. At higher process
speeds, the finished laminate could be delaminated in a
straightforward way, at least in some regions. In the
region of overlapping punched-out portions of the two
paper layers, regions closed with film were formed, on
which the woven structure of the supporting belt showed
itself clearly. In order to prevent this structuring,
high-gloss polished steel strip of 100 mm thickness was
also supplied in these regions. After lamination had
been carried out, the steel strip could no longer be
detached from the polymer film without destroying the
windows.
CA 02591982 2007-06-21
WO 2006/066431 - 36 - PCT/CH2005/000754
Example 2
In a manner analogous to the configuration of example
1, a composite was produced but in this case a
polyamide 12 (PA12) was chosen as polymer. The melt
temperature was 300 C, the input quantity about 45
g/mz. The pair of rolls had a temperature of 50-60 C
and the process speed was 40 m/min. The result was a
multilayer composite which, in regions of overlapping
punched-out portions in the paper, had polymer windows
and which could not be separated without destruction.
The windows had excellent transparency and a mirror-
smooth surface. No turbidity because of
crystallization of the PA12 could be observed.
Example 3
A composite was produced in a manner analogous to
example 2. One paper layer was a security paper having
gray-stage watermarks. The melt temperature was 265 C,
the input quantity was varied from 13 g/m2 (example 3a)
to 35 g/m2 (example 3b). The pair of rolls had a
temperature of 95 C and the process speed was 40 m/min.
The result was a multilayer composite which, in regions
of overlapping punched portions, had polymer windows in
the paper and which could not be separated without
destruction. The windows had excellent transparency
and a mirror-smooth surface. No turbidity because of
crystallization of the PA12 could be observed.
Example 4
A composite was produced in a manner analogous to
example 2. One paper layer was a security paper having
gray-stage watermarks from a cylinder paper machine,
the other paper layer was a plain paper without
watermarks from a fourdrinier paper machine.
CA 02591982 2007-06-21
WO 2006/066431 - 37 - PCT/CH2005/000754
Example 5
A composite was produced in a manner analogous to the
configuration of example 1. One paper layer was a
security paper having gray-stage watermarks. The melt
temperature was 325 C, the input quantity was varied
from 20-35 g/m2. The pair of rolls had a temperature
of 125 C and the process speed was 30 m/min. The
result was a multilayer composite which, in regions of
overlapping punched portions, had polymer windows in
the paper and which could not be separated without
destruction. The windows had excellent transparency
and a mirror-smooth surface.
Measured values
A comparison of some typical mechanical characteristic
values (averages from values measured longitudinally
and transversely with respect to the running direction
of the paper web, testing air-conditioning conditions
23 C, 50% relative humidity) of the multilayer
composites produced in the aforementioned examples is
shown by the following table 2. Typical characteristic
values from example 3 and example 4 are indicated in
table 3. In this case, a standard banknote paper (BN
paper) was used as a comparison.
CA 02591982 2007-06-21
WO 2006/066431 - 38 - PCT/CH2005/000754
Table 2
Conventional Example 1 Comparative Example 2
security example to
paper example 1
Weight per 90 106 105 116
unit area
[g/mZ]
Breaking 80 101 125 103
strength
[N]
Wet 28 61 64 59
breaking
strength
[N]
Wet 35 60 51 57
strength
[% l
Elmendorf 800 1087 1170 1669
tearing
resistance
[mN]
Double 1800 >5000 1623 >5000
fold
number
Process - 70 5 40
speed
[m/min]
Window - Smooth and Matt and Smooth and
quality highly structured higlzly
transparent transparent
Yellowing - unnoticeable noticeable unnoticeable
of the
paper
layers
CA 02591982 2007-06-21
WO 2006/066431 - 39 - PCT/CH2005/000754
Table 3
Example 3a Example 3b Example Standard
4 BN paper
Weight per g/m2 100 79 103 90
unit area
Proportion g/m2 34 13 35 0
of polymer
(L25)
Thickness pm 98 89 106 116
Cobb value g/m2 13/13 14/15 23/12 40-70
*)
Opacity % 89 91 95 94
Burst kPa 400 310 360 350
pressure
Breaking MD 119 123 103 110
force CMD 58 41 62 50
Double fold MD >6000**) >10,000**) >6000**) 2400
number CMD >6000**) 1160 >6000**) 1800
Wet % 65 57 57 45
strength
Ash % 4.2 5.2 6.2 4.1
Elmendorf MD 1130 700 1090 860
CMD 1230 910 1150 980
Window Smooth and Smooth and - -
quality highly highly
transparent transparent
Yellowing None None None None
*) Measure of water absorption capacity. At low values the
susceptibility to soiling decreases
**) Testing stopped
CA 02591982 2007-06-21
WO 2006/066431 - 40 - PCT/CH2005/000754
LIST OF DESIGNATIONS
First paper layer
Second paper layer
Polymer melt
Fishtail die
Pair of rolls
Multilayer substrate
Flattened portion
Polymer layer
Aperture
91 Region in which the polymer layer is exposed only
on one side
100 Viewing window
110 Watermark
120 Penetration zone
201 Non-stop unwind
202 Paper web
203 Draw controller
204 Web edge controller
205 Punching unit
206 Extraction system
207 Dryer
208 Metering device
209 Extruder
210 Infrared radiant heater
211 Die
212 Unwind/splicer
213 Watermark reader
214 Security paper web, watermarked paper
215 Web inspection final control facility
216 Inkjet marking
217 Web accumulator/cutting table
218 Winder
