Note: Descriptions are shown in the official language in which they were submitted.
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INKING SYSTEM FOR INTAGLIO PRINTING MACHINE
Field of the invention
The present invention concerns an inking system for an intaglio printing
machine
printing securities, such as banknotes, checks, passports, ID and other
similar
objects.
Background of the invention
In the field of multicolour intaglio printing it is necessary to fill both the
fine and deep
engraved lines of an intaglio plate with the accurate amount of ink in order
to obtain a
good print quality but, at the same time, minimising the excess of ink
necessary to fill
the fine engravings as well as the amount of ink transferred to the non-
engraved area
of the intaglio plate, thus improving the machine operability and reducing the
ink
consumption.
Examples of printing machines of the prior art are given by US patents
4,516,496,
5,062,359 and 5,899,145.
The state of the art for intaglio printing machines and process provides an
inking
system with a rough regulation of the ink amount along the axis of the
printing
cylinder but with no means for regulation around the circumferential surface
of the
cylinder.
For example, means for more precise regulation are known from US patent
4,604,951 which discloses an intaglio machine having a conventional
configuration
characterised by a duct with ink holding recesses having different depths
corresponding to those of the plate. This machine has never been
commercialised; it
has the following disadvantages:
The machine configuration uses only a direct inking process.
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- The described ink holding recesses on the duct cylinder cannot match
precisely the engraved patterns on the intaglio plate.
- The arrangement duct/blade described requires a continuous cylindrical
surface, not compatible with plate clamping devices. Engraved plates are much
easier to manufacture, install and serve than full cylinders.
High rigidity ink blade cannot be precisely controlled by adjusting screws.
The space between the ink blade and the duct roller will allow a high amount
of ink on the non-engraved surface of the duct, then on the non-engraved
surface of
the intaglio plate, with no ink savings.
- Reducing further the space between the ink blade and the duct will
inevitably
bring the blade in contact with the duct, damaging both the blade and the
cylinder
surface.
Other systems for improving the precision of deposition of the ink and for
reducing
the ink consumption have been developed in the prior art, for example,
European
patent application published under the number 1 442 878. This patent
application
concerns an intaglio printing machine in which the selector cylinders used to
deposit
the ink on a collector cylinder are driven by drives in an independent manner
allowing
to vary the inking print length on the blankets of the collector cylinder.
Another example is disclosed in the European patent application published
under the
number 1 445 098. In this patent application, a blanket cylinder for an
intaglio printing
machine is made with different layers, each with different properties. Said
layers are
engraved and may be lipophilic and/or lipophobic thus achieving a very precise
inking
of the plate cylinder.
It is therefore an aim of the present invention to improve the known machines
and
processes. It is a further aim of the present invention to provide a printing
machine
and a printing process that overcome the defects of the prior art. It is
another aim of
the present invention to provide an intaglio printing machine and process that
are
easier to operate, give superior performance in print quality and ink savings.
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Summary of the invention
According to one aspect, the invention provides an intaglio printing machine
for
printing sheets or webs of securities, comprising at least a feed unit, an
impression
cylinder, a plate cylinder carrying at least one printing plate and an inking
system for
inking the plate cylinder, a printing nip being formed between the plate
cylinder and
the impression cylinder, wherein the inking system comprises at least a duct
for
inking the surface of an engraved selective inking cylinder which in turn inks
the
surface of the plate cylinder via a chablon roller having reliefs
corresponding to
engravings to be inked on the plate cylinder and a wiping system for wiping
the
surface of the selective inking cylinder and recuperating the wiped ink in the
duct.
According to another aspect, the invention provides an inking system for an
intaglio
printing machine, the inking system comprising at least a duct for inking the
surface
of an engraved selective inking cylinder which in turn inks the surface of a
plate
cylinder of the intaglio printing machine via a chablon roller having reliefs
corresponding to engravings to be inked on the plate cylinder and a wiping
system for
wiping the surface of the selective inking cylinder and recuperating the wiped
ink in
the duct, the duct comprising a duct roller for applying ink to the surface of
the
selective inking cylinder, a duct blade cooperating with the duct roller and
an ink
supply formed between the duct blade and the duct roller.
According to a further aspect, the invention provides an inking system for an
intaglio
printing machine, the inking system comprising at least a duct for inking the
surface
of an engraved selective inking cylinder which in turn inks the surface of a
plate
cylinder of the intaglio printing machine via a chablon roller having reliefs
corresponding to engravings to be inked on the plate cylinder and a wiping
system for
wiping the surface of the selective inking cylinder and recuperating the wiped
ink in
the duct, the duct being formed by an ink chamber with an ink spray device for
applying ink to the surface of the selective inking cylinder.
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According to another aspect, the invention provides an inking system for an
intaglio
printing machine, the inking system comprising at least a duct for inking the
surface
of an engraved selective inking cylinder which in turn inks the surface of a
plate
cylinder of the intaglio printing machine via a chablon roller having reliefs
corresponding to engravings to be inked on the plate cylinder and a wiping
system for
wiping the surface of the selective inking cylinder and recuperating the wiped
ink in
the duct, the wiping system including a wiping roller.
Other aspects and features of the present invention will become apparent to
the
persons skilled in the art upon review of the following description of
embodiments of
the invention in conjunction with the accompanying figures.
Brief description of the drawings
A detailed description of the embodiments of the present invention is provided
herein
below, by way of example only, with reference to the accompanying drawings, in
which:
Figure 1 shows a first embodiment of the inking system according to the
present
invention.
Figure 2 shows a second embodiment of the inking system according to the
present
invention with a first configuration of printing machine.
Figure 2b shows a variant of the configuration of figure 2.
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Figure 3 shows another configuration of a printing machine with the inking
system
according to the invention.
Figure 4 shows a further configuration of a printing machine with the inking
system
according to the invention.
Figure 5 shows a multicolor configuration of a printing machine with the
inking system
according to the invention.
In the drawings, the embodiments of the invention are illustrated by way of
examples.
It is to be expressly understood that the description and drawings are only
for the
purpose of illustration and are an aid for understanding. They are not
intended to be
a definition of the limits of the invention.
Detailed description of the embodiments
In figure 1, a first embodiment of the inking system according to the
invention is
shown. In this embodiment, there is a duct, generally shown with the reference
1,
said duct comprising a duct roller 2, an ink adjusting blade 3 for the duct
roller 2 and
an ink supply 4. The duct roller inks a selective inking cylinder 5 which has
an
engraved surface. The surface of the selective inking cylinder 5 can be
directly
engraved or, preferably, the cylinder carries an engraved plate with
engravings
corresponding to the pattern that has to be inked in the given color. In a
manner
known in the art, the inking cylinder comprises a pit 7 in which clamping
means (not
shown) are provided to hold the plate 6 in position.
The inking system further comprises a wiping roller 8, preferably a dry wiping
roller,
which is used to wipe the surface of the inking cylinder 5: thus only ink
present in the
engravings of the inking cylinder 5 remain and the ink present on the non-
engraved
surface of the cylinder 5 is almost completely removed.
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The wiping system further comprises a scraping blade 9 for
scraping the surface of the wiping roller and the ink thus
scraped is recuperated in the ink supply 4 as shown in
figure 1.
Accordingly, the ink supply function of the duct is
separated from the ink thickness adjusting function. The
duct roller 2 supplies an excess of ink to the selective
inking cylinder 5 by means of the duct blade 3. The latter
does not need to be equipped with adjusting screws, because
there is no need of axial regulation of the amount of ink.
The space between the duct blade 3 and the duct roller 2
does not need to be precisely adjusted. As an example, if
the maximum required amount of ink requires a space of say
80 microns, the space can be adjusted with a wide excess
tolerance, say 100-300 microns. This is because the duct
roller 2 has no ink adjusting function. The duct roller 2
is preferably coated with hard rubber or plastic (for
example PVC 500 ShD). It is removable from the press for
maintenance or replacement and is equipped with state of
the art means to adjust the contact with the selective
inking cylinder 5 and is provided with liquid circulation
for thermoregulation. Additionally, it is preferably
equipped with a fast automatic on/off movement actuated at
each revolution in order to avoid that the ink is
transferred to the plate near the bending position.
The selective inking cylinder 5 has the function of ink
adjusting and is equipped, as mentioned above, with a plate
clamping device for an engraved plate 6, usually a chromed
nickel plate. The engraved plate 6 is in rolling contact
with the duct roller 2 and receives an excess of ink from
it, the ink being transferred to both the engraved recesses
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of the plate 6 and the plate surface. After the action of
the dry wiping roller 8, each point of the engraved plate
carries the exact amount (or a slight excess) of ink
required for the intaglio printing process.
The dry wiping roller 8 is above the duct roller 2 and is
in contact with the selective inking cylinder 5 and rotates
in the same direction so that the two surfaces in contact
run in opposite directions. Similarly to a conventional
wiping unit wiping the intaglio plate, the dry wiping
roller 8 removes the excess of ink from the plate 6
surface, leaving ink in the engravings. The excess of ink
is transferred to the surface, of the dry wiping roller 8
and a scraping blade 9 removes the largest part of the ink
from the wiping roller 8 surface. The removed ink falls by
gravity into the duct 1 and can thus be recycled.
Both, dry wiping roller 8 and scraping blade 9, are
equipped with non synchronized axial movement, in order to
even the wear of the roller surface. This is preferably
coated with hard rubber or plastic (for example PVC at 500
ShD) and provided with thermoregulation (known in the art).
The dry wiping roller 8 is preferably driven by an
independent motor, to optimise the rotating speed in order
to minimise the amount of ink left on the non engraved area
of the selective inking plate 6. This is in the range of a
few microns thickness. The scraping blade 9 is preferably
in steel coated with ceramic. The surface of the dry wiping
roller can be alternatively coated with a layer of ink
repellent material in order to increase the amount of
recycled ink which falls into the duct by the combined
forces of gravity and centrifugation.
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In figure 2, a second embodiment of an inking system is
represented. In this embodiment, the duct 10 comprises an
ink chamber 11 with an ink spraying device 12 that sprays
on a duct roller 13. In this embodiment, due to the
direction of rotation of the duct roller, it is not
necessary to use a duct blade as in the first embodiment,
therefore it is possible to directly use an engraved duct
roller 13 (either with an engraved surface or carrying an
engraved plate), thus simplifying the constructions. The
ink spraying is synchronized with the duct roller rotation
in order to avoid ink application in the non-engraved area
of the duct roller and in the roller pit in presence of a
plate clamping arrangement. Over the ink chamber 11, there
is a wiping system with a wiping roller 8 and a scraping
blade 9. Under the scraping blade 9, recuperating means are
provided such as a tank 14 with pump means 15 to bring the
recuperated ink into the circuit of ink being sprayed.
In the embodiment of figure 2, the printing machine
represented is an indirect inking intaglio printing
machine. Accordingly, the engraved duct, with engravings
corresponding to the engravings of a plate cylinder 16,
transfers the ink of the engravings onto a chablon roller
17 with reliefs 18 corresponding to the parts to be inked,
said reliefs 18 transferring the ink to a collector
cylinder 19 before being transferred to the plates of the
plate cylinder 16. The same collector cylinder 19 can
receive the inks of different colors from other inking
units and chablon rollers not shown in figure 2 but similar
to the inking unit represented. The process of indirect
inking in an intaglio printing process is known per se in
the prior art, for example from US patents 4,516,496,
5,062,359 and 5,899,145 mentioned above.
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In figure 2b, a variant of the configuration of figure 2 is
shown. In this variant, identical elements are identified
with the same reference numbers. This variant differs from
the configuration of figure 2 in the fact that the
collector cylinder 19 of figure 2 is removed, thus forming
a direct inking configuration. Accordingly, this variant
comprises a duct 10, with an ink chamber 11 and a ink
spraying device 12 on the duct roller 13. Under the
spraying system, there is a wiping system with wiping
roller 8, and scraping blade 9 and recuperating means, for
example a tank 14 with pump means 15, for the scraped ink.
The engraved duct roller 13, with engravings corresponding
to the engravings of the plate cylinder 16, transfers the
ink of the engravings onto the chablon roller 17 with
reliefs 18 corresponding to the parts to be inked, said
reliefs 18 transferring the ink to the plates of the plate
cylinder 16.
In figure 3, a configuration of a printing machine with the
inking system according to the invention is shown. In this
configuration, the machine has a direct inking of an
intaglio printing plate. The inking part of the machine is
the one disclosed in figure 1, with similar elements
referenced in an identical way. Accordingly, there is the
duct 1, the duct roller 2, the duct blade 3, the duct
roller 2 inking the plate 6 of the selective inking
cylinder 5, which preferably carries an engraved plate 6,
and the wiping roller 8 wiping the surface of the selective
inking cylinder 5. The surface of the wiping roller 8 is
scraped by scrape blade 9 and the ink thus scraped is
recuperated in the duct 1.
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The selective inking cylinder 5 inks then a transfer roller
20 with a deformable surface in order to penetrate the
engravings of the plate 6, said transfer roller
transferring the ink to a chablon roller 21 with reliefs 22
which then in turn deposit the ink directly in the
engravings of a plate of the plate cylinder 23 of the
printing machine.
In a direct inking configuration as shown in figure 3, it
is necessary to use the transfer roller 20 because of the
direction of rotation of the plate cylinder 23.
In figure 4, another configuration of a printing machine is
shown. In this configuration, the machine is an indirect
inking intaglio printing machine. The inking system
represented is similar to the inking system of figure 1 or
3, with similar elements referenced in an identical way.
Accordingly, there is the duct 1, the duct roller 2, the
duct blade 3, the duct roller 2 inking the surface of the
selective inking cylinder 5, which is engraved or carries
an engraved plate 6, and the wiping roller 8 wiping the
surface of the selective inking cylinder 5. The surface of
the wiping roller 8 is scraped by scrape blade 9 and the
ink thus scraped is recuperated in the duct 1.
The selective inking cylinder 5 inks then a chablon roller
24 with reliefs 25 which then in turn deposits the ink on a
collector cylinder 26. The collector cylinder 26 then
deposits the ink in the engravings 27 of a plate cylinder
28 of the printing machine. In this example, the plate
cylinder 28 carries three plates.
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A wiping unit 45, which is per se common in the art of printing machines,
takes off a
minimal excess of ink from the engravings and from the plate surface.
A sheet 29 being printed is shown in this figure 4, said sheet passing through
the
5 printing nip 30* formed between the plate cylinder and the impression
cylinder 31*, as
is common in the art of intaglio printing. Of course, the system according to
the
present invention is also suitable for web-fed printing machines.
The principle of indirect inking in an intaglio printing machine is well known
per se in
10 the art and is disclosed, for example, in US patents 4,516,496,
5,062,359 and
5,899,145 mentioned above.
The configuration of printing machine disclosed in figure 5, corresponds to a
four
color indirect inking intaglio printing machine. It comprises four separate
inking units
30, 31, 32 and 33, each with respective selective inking cylinders 34 to 37,
the
engravings of which (or of the plates they carry) having corresponding
engravings 38
on the plate cylinder 39 according to the principle of the present invention.
Each
inking unit comprises a duct roller 2, an ink supply and a duct blade 3. Ink
is applied
to the selective inking cylinders 34, 35, 36 and 37 and wiped by wiping roller
8 in the
manner described above. Each selective inking cylinders 34, 35, 36 and 37
receives
ink of a different color and has engravings corresponding to the desired
pattern on
the plate of the plate cylinder 39, and the ink is transferred onto the
chablon rollers
40, 41, 42, and 43 of each inking unit.
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In this configuration, the selective inking cylinders 34, 35, 36 and 37 may
have only
the pattern engraved which correspond to the color the selective inking
cylinders in
meant to transfer. Advantageously, in another embodiment the selective inking
cylinders 34, 35, 36 and 37 can be all engraved with the same pattern
corresponding
to the entire pattern of the plate cylinder 39. In this case the entire
pattern receive a
different color on said selective inking cylinders 34, 35, 36 and 37 but the
selection of
ink on each of said selective inking cylinders 34, 35, 36 and 37 is made by
the
chablon rollers 40-43 to transfer only the necessary ink on the collector
cylinder 44.
The advantage of this configuration is that selective inking cylinders are all
identical
which reduces the cost of manufacturing.
Then, the ink of each chablon roller 40, 41, 42, and 43 is transferred onto
the
collector cylinder 44 which in turn inks the engravings 38 of the plate
cylinder 39. A
wiping unit 45, which is per se common in the art of printing machines, takes
off a
minimal excess of ink from the engravings and from the plate surface.
The printing process per se is then carried out on a sheet 40* which passes in
a
printing nip 41* formed between the plate cylinder 39 and the impression
cylinder 42*,
as is known in the art of printing.
The inking system of the present invention has numerous advantages, such as
its
simplicity and the important saving of ink it allows. No important quantities
of ink are
wasted
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anymore since there is a wiping right at the level of the
ink duct rather than on the plate cylinder where all the
colors of ink are then mixed up by the wiping operation and
can not be reused. In the present case, only a minimal
excess of ink is effectively transferred onto the plate
cylinder so a minimal quantity of ink is wiped away and
lost.
Of course, the embodiments described are given by way of
non limiting examples and many variations are possible
within the scope of the claims.
For example, in the configurations of machines shown in
figures 3 to 5, one could use the inking system according
to figure 2.
Preferably, the chablon rollers are prepared in a
conventional way (chablon plate or continuous cylinder). An
advantage of the present invention is that the edges of the
area patterns of the chablon rollers receive a minimal
amount of ink - a few microns thickness. Therefore, the ink
does not build up from the edges to the recessed portion of
the chablon plate and washing is much easier for the
operator.
Preferably, the engraved selective inking cylinders
according to the present invention comprise engravings not
just corresponding to those of the printing plate, but
having lines characterised by:
- identical pattern to that of the printing plate (except
for the necessary specular image, i.e. whether or not the
pattern engraved on the selective inking cylinders has to
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be a mirrored image of the engraved pattern on the printing
plate)
- larger than the engravings on the printing plate, to
ensure registration and compensation of the position
tolerance of the engraved lines on the printing plate
- depth correlated to the depth of the lines in the
printing plate; it is in practice suitable to ensure that
the engravings on the selective inking cylinders have a
depth which is for instance of the order of 30% greater
than the depth of the engravings on the printing plate so
as to guarantee that an adequate amount of ink is
transferred to the printing plate
- engraved using the same technology as for the printing
plate.
In case some areas of the printing plate are provided with
fine engraved patterns (having a depth of less than a few
tens of microns, in particular less than 10 microns), it
may not be necessary to provide the corresponding areas on
the selective inking cylinder(s) with any engravings at
all, engravings being only provided for inking deeper areas
on the printing plate. Indeed, the wiping system may be
adapted to leave a slight amount of ink on non-engraved
areas of the corresponding selective inking cylinder, which
amount of ink can be sufficient to ink fine engravings on
the plate cylinder.
Regarding the patterns engraved on each selective inking
cylinder, it should accordingly be stressed that these
engraved patterns are not strictly speaking identical to
the corresponding patterns on the printing plate. The
expression "corresponding to" used within the scope of the
present description to describe the relationship between
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the engravings provided on the selective inking cylinder(s)
and on the plate cylinder should therefore be construed as
meaning that there is a substantial degree of similarity
between the engravings, but that slight differences in
terms of width, depth and/or position exist. Further, as
mentioned above, parts of the surface of the selective
inking cylinder(s) which correspond to fine engravings on
the plate cylinder may not be provided with any engravings
at all, since non-engraved areas of the selective inking
cylinder(s) could carry a sufficient amount of ink to ink
such fine engravings.
In the embodiments represented in the figures, different
ratio of cylinder diameters are presented. For example in
figures 3 to 5, the ratio collector cylinder to chablon
roller is 3 to 1, whereas in figure 2, the ratio is 2 to 1.
This is of course not to be construed as limiting but as
showing that different configurations are possible,
equivalent and can be chosen according to the
circumstances.
As mentioned above, it is possible for all cylinders having
an engraved surface to be directly engraved or to carry an
engraved plate through clamping means.
