Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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F.ield of the invention
The present invention relates to a plant for
~anufacturing a mold in the form of a thermo-formable,
multiple-impression plastic plate, in particular for
reproducing intaglio printing plates, using an original
plate made of metal which bears an engraved or embossed
design, and by means of compression molding with high-
frequency heating of said plastic plat~, comprising a
struture provided with an electrode-carrying device for
supporting a plate electrode connected to a high-
frequency apparatus, and with a plate-carrying device
for supporting the original plate at a distance from
and opposite to the said plate electrode; at least one
sliding frame for supporting the plastic plate, said
sliding frame being arranged between and movable with
respect to said original plate and said plate electrode
in two perpendicular horizontal directions; and
comprising means for changing the distance between the
said electrode-carrying and plate-carrying devices.
Said intaglio printing plates are intended for sheet-
fed intaglio printing.
Prior art
It is known to manufacture intaglio printing plates for
sheet-fed printing using an original metal plate on
which there has been carefully engraved the image to be
reproduced consisting of engraved lines and zones of
varying depths. Since the intaglio printing plate
arranged on the plate cylinder has several identical
impressions, in particular in the case where bank notes
are printed, arranged in perpendicular rows, the
impression must be multiplied and transferred onto the
intaglio printing plate which is generally made of
nickel. A plant for carrying out this multiplication on
a thermo-formable plastic plate according to the
preamble of claim 1 and as described in the
introduction has already been proposed in the
publication EP-A- 335 830.
In the case of a multiple-impression positive plastic
plate, a known method to obtain the intaglio printing
plate is as follows :
A layer of silver is applied onto the positive plate
and a layer of copper is deposited on the silver-lined
surface by means of electrolysis. By withdrawing the
positive plastic plate, a negative copper plate, also
called a female matrix or lower matrix, which comprises
the engraved impressions, is obtained. The surface of
this negative plate between the impressions must be
machined so as to ensure that it is completely smooth
and continuous. Using this negative copper plate, a
positive nickel plate is reproduced, followed by a
negative nickel plate, which i5 the actual intaglio
printing plate which will be mounted on the plate
cylinder. This plate must also undergo a finishing
treatment so as to ensure, on the one hand, that the
surface between the impressions is smooth and
continuous and, on the other hand, that the rear of the
plate in contact with the plate cylinder is also
perfectly smooth and continuous. In order to increase
the resistance to wear of the intaglio printing plate,
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a layer of chrome is applied.
_ummary of the invention
It is the object of the present invention to improve
the plant for the manufacture of a mold having the form
o~ a multiple-impression plastic plate in such a way
that the impression have a perfect quality without the
risk of deformation of the planeless of the surface of
the plastic plate round about the impression. The mold
in the form of a multiple-impression plate may be a
positive mold or a negative mold and preferably serves
as a base for manufacturing an intaglio printing plate
having a given number of identical impressions.
The plant according to the invention is characterized
in that the said original plate forms a second plate
electrode connected to said high-frequency apparatus,
in that the said first plate electrode has an outline
which corresponds to an envelope of the design of the
original plate and therefore of the impression to be
produced, and in that the edge of the said first
electrode is surrounded by an insulating border, with
the inside edge adapted to the said outline and of a
thickness equal to that of the said first plate
electrode.
The advantages of this plant are as follows : By virtue
of a plate electrode whose outline corresponds to the
envelope of the design and by virtue of the insulating
border surrounding this electrode, the use of high-
frequency heating ensures not only more rapid and more
uniform heating, but also affords that the heating is
better confined to the region of the impression to be
produced. In fact, during the heating of the plastic
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plake, it has proved essential that, as far as
possible, only this zone of the impression to be
produced is heated and not the adjacent regions, in
order to prevent the latter from being deformed during
the molding operation. The plastic plate beyond the
impression zones should remain absolutely plane so that
this multiple-impression plastic plate can serve,
without subsequent treatment of the surface, for
reproducing the intaglio printing plates, as mentioned
in the in~roduction.
If the plastic plate is heated by conventional means,
for example electrically or by circulation of a hot
fluid, it is virtually impossible to prevent this
adjacent zone from being heated as well; for this
reason, with the conventional methods, to prevent such
heating of the adjacent zone, it is absolutely
necessary to limit the temperature of final heating,
which consequently makes it necessary to work with a
greater pressure during the molding. In constrat, with
the plant according to the invention, since the heated
region is limited to the required zone, it is possible
to work with higher temperatures, th~reby enabling a
reduction in the pressure during the molding. Whereas,
according to the conventional methods, a temperature of
about 150 to 170 and a pressure of loo to 200 kg/cm2
are used, with the plant according to the invention it
is possible to heat the plate up to a temperature of
about 200C and apply a pressure of about 20 kg/cm2~
Preferably, at least one of the plate-carrying and
electrode-carrying devices comprises heaking and
cooling means, preferably by circulating a liquid, for
a preheating of the electrodes before these electrodes
are brought into contact with the plastic plate, and
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advantageous that the first electrode having said
outline is carried by an insulating support and that
said first electrode and its border are covered by a
thin insulating layer o~ a rigid materi.al, preferably
S mica.
Preferred embodiments of the plant are defined by the
dependent claims.
The invention relates also to a method of actuating the
plant according to the invention, which is characterized
by the following steps :
a) a plastic plate made of thermo-formable
material having essentially the dimensions of the mold
required, is prepared;
b) a first plate electrode, the outline of
which corresponds to the envelope of the design of the
original plate and therefore of the impression to be
pxoduced, is prepared;
c) the edge of the said first plate electrode
is surrounded by an insulating border, the inside edge
Of which is adapted to the said outline and the
thickness of which is equal to the thickness of the
said first plate electrode;
d) the said plastic plate is placed, in an
adjusted position corresponding to the location of the
first impression to be produced, between th~ first
plate electrode and the original plate which is used as
a second plate electrode;
e) the two electrodes are brought near to the
said plastic plate and the latter is subjected to
hiyh-frequency heating by producing, between the two
electrodes, a high-frequency field for a given period
of time until the plastic plate has reached a
temperature suitable for molding;
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f) the first impression is produced on the
plastic plate by compressing the latter by applying the
molding pressure;
g) the plastic plate is cooled, while the
molding pressure is maintained;
h) the electrodes are separated and relative
displacement is effected between, on the one hand, the
plastic plate and, on the o~her hand, the electrodes,
successively in the ~ther adjusted positions
corresponding to the other impressions to be produced
and, in each position, the steps e) to g) are repeated
in order to reproduce th~ next impression.
A pre~erred variant of this method is characterized
in that the electrodes are preheated before being
brought into contact with the plastic plate.
Brief descri~tion of the drawin~s
Two exempl~ry embodiments of the plant will be
described with the aid of the accompanying drawing.
Figure 1 is a perspective view of a first form of
e~bQdiment of the pLant for implementing the method.
Figure 2 is a partial and enlarged side view of
1;he plant.
Figure 3 is an enlarged side view of a variation
of ~he pla~t.
25Figure 4 is a plan ~iew of an original plate
~howing a diagrammatic illustration o the design and the
outline, or periphery, which surrounds the zone of design
and thi~ outl~ne is of course imagina~y and h~s been
~hown only for the sake o th~ description.
30Figure S shows the plate elec~rode having an
outline corr~sponding to that of the design.
~ Figure 6 is a view of the same electrode, but
plac~d on an insulating support and surrounded by an
insulating border.
35Figure 7 is a sectional ~iew along VII-VII of
F~g~re 6.
Figure 8 shows a second form of embodiment of the
plant~ illustrating only the ele~ents essential for the
in~ention~
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5~
Figure 9 is a diagra~matic view in the direc~-ion
of the arrows IX-IX of Figure 8.
Fig~re 1~ is a sectional view of the electrode-
car~ying device of Figures 8 and 9, along X-X of Figure
5 9, to an enlarged scale.
Figure 11 is a view similar to Figur~ 6 e~cept
for the fact tha~ the shape of ~he electrode does not
correspond exactly to the outline of the design, but ~o
the rough envelope thereof and ~hat the border covers
the entire insulating support and forms one piece with
the latter.
Figure 12 is a sectional view along XII-XII of
~igure 11.
Description of the preferred_embodimen~s
For the sake of greater clarity, first the plants
for implementing the method and subsequently ~he method
will be described.
The plant according to Figure 1 comprises a
structure 1 serving as a base for the remainder of the
plant. A first sliding frame 2 displaceable in a hori-
zontal direction F2 is mounted on the structure 1. Asecond sliding frame 3 is mounted inside the sliding
frame 2 and is displaceable inside the latter in a
direction F3. A plastic plate 4, which is fixed by clamps
3a and will form the multiple-impression mold, is placed
inside the second sliding frame 3. A few impressions 23
are indicated in Figure 1.
In the middle of the region in which the first
sliding fr~m~ 2 moves, and below the sliding plane, is
arranged the electrode~carrying device. As shown in
Figure 2, this device comprises a support saddle 5
integral with the structure 1, on which there is arranged
an insulati~g plate 6 supporting a heating and cooling
device 8 consisting of a flat metal box in which a liquid
can circulate and which is provided for this purpose with
two pipes 8a and 8b for the inlet and outlet of the hot
or cold liquid as required. ~n insulating,plate 26, on
which there is arranged an insulating support 25 carrying
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a first plate electrode 7, ~ests on this heatin~ a~d
cooling de~ice ~ The arrangement and the configuration
~f this electro~e ~ will ~e describ~d in greater detail
on the bas~s of Figures 4 ~o ~
Vertically in line withthe electrode thereis lo-
catedaplate-carrying d~vice for fixing the orig-~nalplatel9
which, in the example under consideration, has an en-
graved design on it. Thi~ original plate 19 is used as a
second el~ctrode. The said plate-carrying device is
installed by means of a framework 10 which, in the
example illustrated in Figure 1, comprises four slanting
legs and an llpper plate 9. A douhle-acting jack 11 is
fixed onto this plate 9 and the rod 12 of the piston of
the said jack passes through the plate 9 and carries, on
its bo~tom end, the plate-carrying device. The latter
consists of a support plate 13 provided with two guiding
rods 14, 15 extending parallel to the rod 12 of the jac~
11 and passing through the upper plate 9. The actual
plate carrisr carrying the original plate 19 is suspended
via four thr~aded rods 16 provided with nuts 17 for
adjusting the level. This plate carrier constitutes both
a heating and cooling de~ice 18 consisting of a flat
metal box provided with two pipes 18a and lBb serving as
an inlet and outlet for the hot or cold liquid as re-
quired.
A chamber 20, inside which a relative vacuwm maybe created, is ~rranged below the device 18. This chamber
20 consists of a bellows, the top end of which is in-
tegral with the ~evice 18 and the ~ottom end ~f which is
in close contact with the plastic plate 4.
Finally, on a console 21 there is arranged a
high-frequency apparatus 22 as well as various controls
enabling, for example, the sliding frames 2 and 3 to be
displaced and the jack 11 to be controlled. In the
example illustrated in Fiyures 1 and 2, the electrode 7
is connected to the live terminal of this high-frequency
apparatus 22 whereas the original plate 19 is grounded,
i.e. is in contact with the device 8 made o metal and
the other elements of the metal structure l.
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Figure 4 shows the original plate 19 with an
engra~ed design l9b which extends o~er an irregular zone
marked by an ~utline forming the periphery 19a of this
engraved zone. Of course, this outline does not exist in
reality, it is indicated in Figure 4 in order to il-
lustrate the boundary of the design clearly.
Figure S shows the electrode 7 cut in such a
manner that its outline 7a corresponds to the envelope
l9a. This electrode 7, which is preferably a sheet of
copper about 0.5 m~ thick, is fixed, according to Figures
6 and 7, for example by bonding, onto an insulating
support 25 about 1.5 to 2.0 mm thick, and is surrounded
by an insulating border 24 which is bonded onto the
insulating support 25 and the inner edge of which has the
shape of the outline of the ~lectrode 7 and therefore
fits around the edge of the latter. The border 24 has the
same thickness as that of the alectrode 7 J their surfaces
are therefore in the same plane (Figure 7).
The insulating support 25 and the border 24 are
made of an electrically and thermally insulating mater-
ial, preferably glass fibre-reinforced silicone, and cut
ou~ of an elastic strip. In the example under cons~dera-
tion, ~he border 24 is a part dïstinct from the insu-
lating support 25 and only surrounds the region adjacent
to the electrode 7 without covering the entire surface of
th4 insulating suppor~ 25, the dimensio~ls of which
correspond approximately to the original plate 19 or are
slightly larger. The minimum width of the ~order 24
should be about 5 mm to ensure ~oth good support for the
plastic plate 4 axound the Lmpression during the molding
and gcod electrical and thermal insulation, so that the
heating is concentrated exclusively on the zone defined
by the outline 7a of the electrode 7. Under these condi-
tions, any deformation of the surface of the plastic
plate around the impression is pre~ented and perfect
pl~neness beyond the impressions is guaranteed, this
planeness being essential for the subsequent manufactur-
ing of the intaglio printing plates.
Since the insulating support 25 is flexible and
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relatively thin, pro~ision h~s been made, according to
Figure 2, for a further insulating plate 26 made of rigid
material, for example bakelite, 4 to 5 mm ~hick, which is
therefore placed between the device 8 and the insulating
support 25 to prevent dissipation of the high-frequency
energy and to provide good support.
The electrode 7 can be connected to the high-
frequency apparatus 22, not shown Ln the drawings, via
the insulating support 25.
According to the variation of Figure 3, a rigid
insulating thin plate 27, preferably made of mica, having
a thickness of about 0.7 to 1.O mm, is placed on the said
electrode and its border 24. This arrangement ensures a
perfect impression and prevents the join between the edge
of the electrode 7 and its border affecting the quality
of the impression.
Figures 8 to 10 show a second form of embodiment
of the plant, in which it is the original plate 19 which
is connectsd via a copper strip 28 to the live outlet of
the high-fre~uency apparatus 22. The jack 11 is installed
on the framework 10 by means of plates 9, 9a, and the
supporting plate 13, provided with the guiding rods 14,
15, is suspended from the end of the rod 12 of the piston
of the said jac~ (Figure 9). Fixed to this supporting
plate 13, by means of an electrically and thermally
insulating plate 6', is the plate carrier consisting of
the heating and cooling device 18 provided with the pipes
18a, 18b. The fixing of the original plate 19 is effected
by means of a supporting frame 18c in metal contact with
the device 18 in such a manner that the device
18/original plate 19 assembly form ~he high-poten~ial
electrode in this case, the copper strip 28 being fixed
to this frame 18c. The plant according to Figures 8 and
9 works without a vacuum chamber.
As far as the electrode carrier is concerned, it
again comprises a heating and cooling device 8 consisting
of a flat box which is provided with two pipes 8a, 8b for
the circulation of the hot or cold liquid and is
positioned, without any insulation, on the support saddle
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S by means of a ~hree-point support.
Figure lO shows the exact axrangement of this
electrode carrier In this case, provision is made for a
me~al pla~e 29 supporting the insulating plate 26 on
which there is ar~anged the insulating support 25 carry-
ing the electrode 7' surrounded by the insulating border
24 which forms one piece with the said support 25. The
entire assembly is preassembled ~y means of s~rews 30
which pass through these elements and the bottom end of
which emerges in a housing 29a of the metal plate 29 and
is screwed into a nut ~Oa. The head of the ~crews 30 is
embedded in conical holes ~b formed in the electrode 7~
so that these screws 30 are flush with the surface of the
electrode. A mica plate 27 is also provided on top of the
electrode 7~and its border 24. The metal plate 29 has
inclined edges enabling it to be fixed to the device 8,
together with all of the other elements, by means of
winches 31 which likewise have inclined faces and clamp
the said inclined edges of the ~etal plate 29. ~ith ~his
arrangement, the electrode 7' is grounded ~y means of the
screws 30, the device 8 and the structure.
The insulating part forming the support 25 and
the border 24 is preferably a flexible plate made of
silicone, with a thickness of 2 to 3 mm, on the surface
of ~hich a recess with the shape of the outline of the
electrode 7' has been made. The depth of this recess
corresponds to the thickness of the electrode, na~ely
about G.S mm. For this reason, the border 24 covers the
entire insulating support 25(Figure 12).
As shown in Figure 11, the outline 7a of the
elec~rode 7I does not exactly match in this case the de-
tails oftheoutline ofthe engraved design,shown inFigure4
andrepresented.in dottedlines,butcorresponds toarougher
envelope ~9a'
Of course, these pl~nts are only exemplary
em~odiments and, instead of only the plastic plate
moving in the two direction F2, F3, the original plate 19
and the entire plate-carrying device together with the
jack 11 and the electrode 7, 7' may, either move in a
hori~ontal direction FZ or F3, and in this case the
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plastic plate 4 is displaceable in the other direction F3
or F2, or move in both directions, and thus the plastic
plate 4 is fixed. Moreover, the heating and cooling
devices 8, 18 may be of another type.
S The method will be described with the aid of the
plant according to Figures 8 to 12.
A metal original plate 19 is prepared, this plate
having on it engraved lines of varying depths constitut-
ing the desi~n to be reproduced, and it is fixed to the
plate carrier consisting of the heating and cooling
device 18 by means of the insulating plate 6'.
A copper sheet forming the electrode 7' is
prepared, this sheet being cut according to the envelope l9a'
of the design, and it is fixed in the hollow of the
lS insulating support 25 in such a way that it is surrounded
by the border 24 (Figure 11).
A plas~ic plate 4 made of material being thermo-
formable by means of molding and compression, for example
COBE~ P.V.C., and having practicaLly the same dimensions
as the intaglio printing plate required, is prepared.
This plastic plate 4 is arranged in the sliding frame 3
and held in position by adjustable clamps 3a enabling it
to be kept uniformly tensioned inside the sliding frame
3 (Figure 1). By means of two sliding frames 2 and 3, the
plastic plate 4 is brought into a ~irst adjusted position
which corresponds to the position of the iirst Lmpression
23 (Figure 1). In this position, the zone to be deformed
by molding is located between the electrode 7' and the
original plate 19 which is located vertically above the
elec~rode 7'.
The electrode 7~as well as the original plate 19
which itself forms an electrode are, in the raised
position of the original plate 19, preheated by circulat-
ing hot water thro-lgh ~he two devices 8, 18 until these
electrodes reach a temperature of between 40 and 50C, in
particular 45C, which generally takes about 2 minutes.
This preheating operation enables a better qualiSy
impression to be obtained, since the problems of varying
expansion of elements in contact are avoided, expansion
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-~ which could adversely affect ~he impression.
Once the preheating te~pera~ure is reached, ;the
oxiginal plate lg i5 lowerèd, by means of the jack 11,
until it is -in contact with the plastic plate 4 and,
while applying a slight pressure o~ t~e order of 5 kg/em2,
the high-frequency field is applied via the two elec-
trodes until ~he plastic plate 4 reaches a temperature of
about 200~C. To this end, a frequency of, for example, 27
MHz applied for 15 to 20 seconds is used. '~ests carried
out have shown that the elec~rodes, the insulating
support 25 and the insulating border 24 reach a temper-
ature of only 40 to 50C. The temperature of 200aC of the
plastic pla~e 4 is higher than that used with ~he methods
known hitherto and enables a lower pressure to be sub-
s~quently applied, thereby preventing deformation around
the actual impression zone.
Once this temperature i5 obtained, the molding
pressure to obtain the impression, for example of the
order of 20 to 25 kglcm2, i.e. 5 to 10 ti~es less than
for known methods, is exerted by means of the jack 11,
the power supply of the electrodes is interrupted, and
while maintainîng this molding pxessure, the original
plate 19, the electrode 7' as we:ll as the plastic plate
4, are cooled by circulating cold water in the devices
8, 18~ When the original plate 19 has reached room
temperature, i.e. about 20C, which takes roughly 2 to
2.5 minutes, the pressure is released and the original
plate 19 is separated from the plastic plate 4 by
raising the plate-carrying device. The operations to
produce a single impression thus take about S minutes.
Then~ the plastic plate 4 is moved into a second
adjusted position, displacement being effected either in
the direction F2 or in the direction F3, and the same
operations as above are restarted in order to obtain the
second impression and so on, until as many impressions,
lines and columns as req~ired have been applied onto the
plate 4.
A mold in the form of a multiple-impression plate
4 (Figure 1) is thus obtained. Since an engraved ori~in-
al plate was used, the mold obtained by the method is a
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positive plastic mold. Nevertheless, a negative plastic
mold would ~e obtained using the same method, if a
positi~e original plate which, itself, would have been
reproduced using an engraved prLmitive plate,were used.
S Furthermore, where appropriate, it is possible to
leave out the preheating operation.
` If the plant according to Figures 1 ~o 3 is used
for implementing the method, after the preheating phase,
the plate-carrying device is lowered until the bottom end
of the bellows of the chamber 20 comes into contact with
the plastic plate 4 and an approxLmately 80% vacuum is
created in this chamber with the aid of a device not
shown. Molding under vacuum could have, under certain
conditions, advantages, but is not necessary. Of course,
lS after cooling and before mounting the original plate 19,
the chamber 20 is connected to the external atmosphere.
Instead of the plate~carrying device being
lowered in order to apply a compressive force on the
plastic plate 4, it is possible to envisage that the
plate carrier is fixed and that the electrode 7 with its
support are raised in order to apply the pressure.
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