Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
WO 90/14953 2 0 4 ~ 411 PCr/GB90/00759
MAt'~Tl~E AND METHOD FOR IMPRESSING RF~T.F.~.SART.~ FOIL ON TO A
MOVING WEB
This invention relates to the transfer of foil from a
carrier to a moving web such as a web of paper by means of
impression dies and particularly concerns the transfer of
foil in the form of a device or discontinuous pattern on to
bank notes or other security documents which are preprinted
on a moving web.
It is generally known to impress thermally releasable foil
from a carrier on to paper. The process requires an
impression die, which may be mounted within or form part of
a heated platen, which may be in cylindrical form, the
foil, which is typically a metal foil carried on a
substrate from which it can be released by the application
of heat and pressure, and a means for applying pressure to
the paper so that the foil released from the carrier is
transferred on to the paper. The particular characteristics
of the material employed in such a technique are not
important to the present invention, which may in general be
applied to any form of foil which can be transferred on to
paper in the manner described: such foils include
holograms, diffraction gratings and various thin film
devices as well as met~llic foils. The web may consist of
other materials such as polyesters.
The technique mentioned requires the application of heat
and/or pressure for a substantial time dependent upon the
heat and/or pressure employed. The foil, the die and the
paper must be relatively stationary for a significant period
of time required to ensure that the foil is released from
the carrier and is securely impressed on the sheet of paper.
It is accordingly comparatively easy to impress foil using
WO 90/14953 PCT/GB90/00759
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such a technique on to documents which are presented in cut
sheet form.
The present invention however concerns the transfer of foil
on to a moving web which may be of paper or other materials
such as polyesters. For example, it is common to print bank
notes or other security documents on a web which moves at
approximately 75 metres per minute, and it is inherently
difficult to ensure that the various elements remain
relatively stationary for the period of time necessary for
transfer of the foil.
A natural solution to the problem is to entrain the foil to
move in the same direction as the web, for example by
providing a cylindrical platen including a die and moving
the foil carrier in synchronism with the web around the
platen and applying pressure to the web while the foil
carrier is disposed between the die and the web. Such an
arrangement can be made to operate satisfactorily for the
purpose of transferring foil on to the web. However, such a
technique is unsatisfactory for transfers of separate
devices hec~ e the devices are spaced apart at least by the
distance between successive doc~"el~Ls on the paper and
accordingly such a technique is very wasteful of foil, and
is expensive at least in terms of the waste of time
associated with the changing of spools of foil.
The present invention aims generally to provide a compact
and versatile machine in which, at least in preferred
forms, there is a substantial economy in the use of foil.
However the invention includes further i",~luvements which
will become apparent from the following description.
WO90/149S3 2 0 4 5 411 PCT/GBg0/0075g
Summary of the Invention
The invention is based on the transfer of foil from a
carrier tape to a moving web by pressing the web against a
die which may be carried in a rotating cylin~er, the foil
carrier being fed between the die and the web and being
transported between successive transfers in a direction
generally transverse to the movement of the web.
The important advantages of this technique are that the
transporting of the foil carrier is not constrained by the
movement of the web and it is possible to achieve a much
greater economy in the use of the foil.
In particular, several dies may be carried on a cylinder
which is rotated in synchronism with the movement of the web
and the tape may be transported in a direction which is
inclined relative to the direction in which the dies are
spaced apart so that different dies transfer foil from
regions which are spaced apart both along and across the
strip and preferably, in a row aligned obliquely to the
strip. Thus the tape may be transported through a
comparatively short distance between transfer operations and
the wastage can be substantially reduced. The foregoing
technique is particularly suitable for impressing one device
on each of a multiplicity of bank notes or security
documents which are preprinted on the web in a multiplicity
of rows or columns spaced apart across the width of the
web.
Pressure may be applied to the web by means of a pressure
roller or band which moves in corresp~n~n~e with the
movement of the web. The band or roller may be driven but
may idle in engagement with the cylin~r. In particular, a
band may be carried between rollers or gears which tension
WO90/14953 PCT/GB90/00759
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the band and drive it so that it 1. -inc stationAry relative
to the paper in the region where the band extends around the
said cylinder. The said roller or band may also enable the
printing cyl;n~r to be driven by the web by virtue of the
friction between the paper and the cyl;nder.
According to one aspect of the invention there is provided:
apparatus for transferring foil from a carrier tape to a
moving web comprising a rotatable cylinder including at
least one die, means for traversing the web around the
cylinder, means rotatable with the cylin~r for transporting
the tape generally lengthwise of the cylin~ler and over the
position of the die, and means for applying pressure to the
web.
The means for transporting the tape may comprise a supply
mechAni~m and a take-up mechAnicm which are carried on an
assem~bly which rotates with the said cylinder.
The supply mechanism may comprise a spool and means such as
a brake for maintaining tension in the tape, and the take up
mechAnism may comprise a spool which includes or is
associated with means operable to index the tape for a
predetermin~ longitl~inAl movement each time the take-up
me~hAni~m passes through at least one predetermined position
in an angular sense of rotation of the rotating cyli~r.
For ~xA~rle, there may be provided a circular track engaged
by a follower which is actuated by cam action to operate a
pawl and thereby cause an incL~...enLal movement of the
tape.
As mentioned hereto, the rotatable cylin~r may include a
set of impression dies spaced apart along a line which
extends generally Axi~lly of the rotating cylin~er, and the
means for transporting the tape may include means for
WO 90/14953 PCr/GB90/0075g
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guiding the carrier in a direction such that the impression
dies engage the tape from locations which are spaced both
longitn~;n~lly along and transversely across the tape.
There may be a plurality of sets of such dies, angularly
spaced around the cyl ;n~r: each set is preferably
associated with a correspon~ing transport mech~n;~m for
transporting foil past the respective set of dies.
WO 90/14953 PCT/GB90/00759
Description of the Drawings
Figure l is a general view of a foil transfer machine,
showing mainly the path of a web and the various rollers and
drive mechAni~m;
Figure 2 illustrates a printing cylinder and associated foil
transporting mech~ni~m;
Figure 3 illustrates a tape take-up reel assembly;
Figure 4 illustrates a tape supply reel assembly;
Figure 5 illustrates part of the take-up assembly;
Figure 6 illustrates a further detail of the printing
cylin~r;
Figure 7 illustrates a sectiQn through part of the printing
cylinder;
Figure 8 is another view of the part illustrated by Figure
7;
Figure 9 illustrates the region of a die in greater detail;
Figure lO is another view of the region illustrated by
Figure 9; and
Figure ll illustrates a section through the take-up
assembly.
WO90/14953 PCT/GB90/00759
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Detailed Description
The following description is a description of a suitable
embodiment of a foil transfer unit which is inte~e~ for
transferring foil in small devices or patterns on to
particular areas of a moving web of paper. The invention is
intended for use in the production of impressed foil devices
on bank notes or other security documents though the
invention may have utility in other contexts.
The general technique for transferring foil, sometimes known
as "blocking", is well known. It requires a heated die
which may for example be mounted in a heated platen, and a
th~r~l ly transferable foil, which is normally a metal
l~min~ secured releasably to a substrate. Pressing paper
against the die, the foil with its substrate being
interposed, for a period of time which depends upon the
temperature and pressure, is sufficient to transfer the foil
from the substrate to the paper in the pattern determined by
the die.
It is, as remarked previously, necessary for the successful
transfer of foil to ensure that the die, the carrier (i.e. a
tape) and the paper are relatively stationary for a
substantial period of time. Normally a fourth element, a
means of applying pressure to the back of the paper, has to
be stationary relative to the other elements as well. It is
known and not difficult to effect foil transfer from dies of
any particular size or shape on to a sheet of paper which
may be kept stat;o~ry for the period of time necessary for
the transfer of foil.
WO9O/14953 PCT/GB9O/00759
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Bank notes and other security documents are made by two
generally different types of machine. The documents can be
printed on sheets or they may be printed on to a web. At
some stage a web is cut up into sheets but normally there is
a distinction between a cut sheet machine and a web machine.
In a cut sheet m~Chin~ most of the printing processes are
performed on the separate sheets on which there is norm~lly
an array of bank notes or other security documents. In a
web machine almost all the processing and printing is
performed on a moving paper web. It is for the latter type
of machine that the present invention is particularly
int~n~. Typically the documents are printed several rows
wide and the web of paper moves continuously through a
multiplicity of stages which are required for the printing
of a bank note or other security document. A web machine of
this general character is of known construction and will not
be described herein. For the purposes of the present
invention it is only important to understand that the web of
paper which traverses the foil transfer unit is normally in
continuous motion, typically at about 75 metres per
minute.
Figure 1 illustrates the path of a paper web through one
embo~imqnt of a foil transfer unit according to the
invention. Figure 1 shows mainly the web, the rollers over
which it passes, and in general schematic form, the drive
arrangement for the rollers.
An arrow 1 shows the direction of movement of a web 2 of
paper entering the foiling unit near the bottom thereof. The
web passes over a fixed roller 3, a dancing roller 4, a
- fixed roller 5 and an additional fixed roller 6. The
dancing roller 4 is mounted on an arm 7 disposed on a pivot
WO90/14953 PCT/GB90/00759
2a~s~ll
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8 mounted on support 9. Means in customary form may be
provided for measuring the angular position of the arm 7.
The arm 7 and its roller 4 constitute a tension arm, the
angular position of which depends upon the loop of web
formed between the rollers 3 and S. The rate of change of
the length of this loop ~pPn~ on the difference between
the speed of the web entering the foiling unit and the speed
of a roller 13 which pulls the web into the foiling unit and
may be used to control the speed of the web. After leaving
the roller 6 the web passes over a steering unit comprising
a roller 10 and a roller lOa which are mounted one at each
end of a pivoted chassis 11 which can be rotated about a
vertical axis so as to maintain the correct lateral position
of the web within the foiling unit.
From the steering unit the web passes around a roller 12 and
then a draw roller 13, which is driven by means later
described from a motor 26. From the draw roller 13 the web
passes over a fixed roller l4, and then to an input guide
wheel 15 disposed at one end of a circumferential path, in
this example a semicircular path 16, ext~n~i ng around a
printing cylinder 17. The end of the path is defined by a
second guide wheel 18 around which the web passes,
procee~ing thence to a roller 19. The web, shown at 2a,
leaves the unit near the top of the machine.
Associated with the draw roller 13 is a larger wheel 13a
which is connected by a flexible drive coupling 20 to a
wheel 21 which is in fixed rotation~l relationship with a
larger wheel 22 linked by a flexible drive coupling 23 to a
wheel 24. The coupling 23 is tensioned by jockey wheel 25.
The wheel 24 is driven differentially relative to a wheel
24a by a variable ratio derived from a gearbox through which
WO9O/14953 PCT/GB9O/00759
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wheels 24 and 24a are coA~iAlly connected. The purpose of
this mechanism, which varies the speed of the draw roller 13
relative to the impression cylinder 17, is to synchronise
the pitch of the ~Le~,inted web 2 to the pitch of impression
dies on the printing cylin~Pr 17. The angular position of
the cyli~Pr 17 is monitored by an encoder, and the position
of the preprinted web coming off draw roller 13 is monitored
using an optical sensor. An error in the web's position
relative to the correct position is used to cause a change
in the gearbox ratio. This results in a change in tension
in the web between the draw roll and the printing cylinder
in a sense to eliminate the error. For convenience this
mechanism, which is in generally known form, is not
illustrated in Figure 1. The wheel 24a is linked by means of
a flexible drive coupling 27 to a wheel 26 driven by the
output shaft of a motor M, a wheel 28, and two wheels 29
and 30 which tension the coupling 27. The wheel 28 rotates
with a pinion 31 which meshes with a pinion 32 that is fixed
to rotate with a wheel 33.
The printing cylinder 17 is driven, in this embodiment, by
at least one band and preferably at least two bands 34, 37
which may apply pressure on the rear of the paper so as to
urge the paper against the dies which are carried by the
printing cylin~Pr, as will be described later. The belt 34
is driven by the wheel 33, and passes over the roller 18,
around the path 16, over the roller 15, around a tensioning
roller 35 which is mounted on a moveable carriage 36 which
is adjustable to alter the tension in the band 34. Another
drive and tensioning belt 37 is also carried on the roller
33, at a position A~iAlly displaced from the belt 34, and
passes over roller 18, around path 16, over roller l5 and
WO 90/14953 PCI/GB90/0075g
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over roller 38 which is mounted on carriage 39, which is
adjustable to adjust the tension in the band 37.
The bands 34 and 37 may each be called an impression band
because they serve to urge the web towards the cylinder in
the manner of an impression roll which presses a sheet of
paper against a printing cylin~er. The bands 34 and 37 are
preferably made of a synthetic rubber or plastics material.
They may each have a flat, smooth surface on the side which
is to face the cylinder 5 and each may have its rear face
formed as a toothed rack engaging co-operating gear teeth on
the associated wheels so that the bands 34 and 37 are driven
without slip.
Alternatively, pressure may be applied to the web where it
passes over a die by a roller fitted in place of roller 15.
Such a pressure roller may either be an idler or be
driven.
Figure 1 also shows dia~L --tically a tape supply cassette
assembly 49 which is mounted to rotate with the printing
cyl;n~Pr 17. Also mounted for rotation with the printing
cylin~Pr is a take-up assembly, described with reference to
Figures 3 and 5.
Figure 2 illustrates one er-~Aiment of a printing cylinder
17. This cyli n~r includes in this example a set of dies
51, 52 and 53. These dies are in this embodiment aligned
along an axis which extends parallel to the axis of the
printing cyl in~9r. Each die can be held in a forward or
impression position by a conical cam, the retraction of
which allows the dies to retract under the action of return
springs, to be described later.
WO90/14953 PCT/GB90/00759
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Typically, there may be a multiplicity of sets of dies
spaced apart around the printing cyl in~r which may
correspond in circumferential extent to an integral nllmh~r
of lengths of preprinted sheets, including the spacing
therebetween, on the web.
As indicated in the foregoing, the web of paper is wrapped
around a substantial angle of the printing cylinder. The
printing cylinder is driven in synchronism with the web of
paper so that each row of dies is brought into register with
the locations on the documents in a particular row where it
is desired to produce the foil devices. Since the printing
cyl;n~r and the paper web are driven synchronously, the
paper will be station_ry relative to the dies and the
impression bands over a substantial angle of move,..ellt of the
printing cylin~er.
Carried at one side of the printing cylinder is a cassette
assembly 42 including a spool 43 which takes up the foil
transfer tape 48. The tape is aligned in a direction which
is inclined relative to the line 54 along which the dies 51,
52 and 53 are disposed. The width of the tape should be
such that all the dies in a given set can engage the carrier
tape at the same time.
In order to control the longitn~inAl transport or in~xing
of the tape 48 there is a circular track 45, of which only a
small segment is shown in Figure 2. This track 45 is
coaxial with the axis of rotation of the printing cylin~er
17 and is engaged by a roller follower 46 mounted on a lever
47. The track is shaped to cause movement of the lever 47,
and thereby in~ing of the ratchet wheel and incremental
transport of the tape 48 at some suitable time when the tape
WO 90/14953 PCI/GB90/00759
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and dies are not in proximity to the web, that is to say at
some point in the semicircular arc opposite the path 16.
Figures 3, 5 and 11 show the take-up assembly 42 in greater
detail.
A cassette 58 is mounted on a holder 57. The spool 43 is
associated with two pinch rollers 44 and 55, there being a
small entrance guide roller 56 round which the tape enters
the drive system from an elongate guide 59 connecting the
supply and take-up assemblies and serving to guide the tape
48 between the printing cylin~r and the web. This guide is
described later with reference to Figures 7 to 10.
As is shown in Figures 5 and 11, the roller 44 rotates with
a coAx;Al ratchet wheel 63, which is controlled by a pawl 64
mounted by a pivot 67 on the arm 47. The ratchet wheel is
adjacent a pulley wheel 63a. The adjacent side faces of the
ratchet wheel 63 and the wheel 63a are in frictional
engagement. The wheel 63a is coupled by means of a flexible
band 65 to a wheel 66 which is mounted on the axis of the
spool 43. This arrangement forms a slipping drive to
maintain foil tension on the take-up spool. Each lifting of
the follower 46 rocks the lever 47 about its pivot 47a
(shown diagrammatically in Figure 5) and causes the pawl to
push the ratchet wheel 63 and accordingly to produce one
increment of longitll~inAl movement of the tape 48.
Referring now to Figures 7 and 8, the guide 59 has a
shallow, inverted U section. The guide fits into an oblique
slot 100 in the cyli n~r 17 and is held in place by tabs 101
held by screws 102 and ext~n~ing over the margins 103 of the
guide 59. For most of its travel adjacent the cylin~r 17
WO90/14953 PCT/GB90/00759
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the tape passes through the narrow passageway 104 between
the underside of the guide 59 and the bottom 105 of the slot
100 .
Figure 4 illustrates schematically a tape supply mechAni~m
49. This comprises a spool 50 which is- mounted in a
cassette 60 disposed in a holder 61. The tape 48 is wound
off the tape supply spool, passes round a small guide roller
62 and is pulled, by the take-up reel ~chAni sm previously
described, along and adjacent the guide 59. The spool 50
preferably includes a brake to maintain tension in the tape.
Figure 6 is a simplified sectional view of the printing
cylinder 17. The cylinder is mounted on two half shafts 68
and 69, which rotate on bearings 70 and 71 respectively.
Each tape take-up assembly 42 is mounted on the half shaft
69 and is located by means of a spigot 72 engaging an
aperture 73 in the adjacent end plate 74 of the cylin~er 17.
Likewise each tape supply assembly 49 is mounted on the half
shaft 68 and is located in position by means of a spigot 75
engaging an aperture 76 in the adjacent end plate 77 of the
cylin~r 17.
The cylinder 17 includes as previously mentioned at least
one row of retractable dies although in practice there are a
plurality (e.g. twelve) of rows of dies each associated with
a tape supply assembly and a take-up assembly. For
convenience only one die is shown in Figure 6. The region
of the die 53 is illustrated in greater detail in Figures 9
and 10.
WO 90/14953 PCr/GB90/0075g
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Figure 9 is a sect;o~l view of the die assembly in a plane
lengthwise of the guide 59 and Figure 10 is a view in a
plane transversely of the guide 59.
As is shown in Figures 9 and 10, a die assembly is mounted
in the peripheral wall 78 of the cyl;~r 17. The wall has
a circular aperture 79 which includes an intern~1 annular
shoulder 80. A body 81 has a tubular part 82 which fits
into the aperture 79 and an ~nmll ~r flange 83 which abuts
the shoulder 80. The flange may be secured to the wall 78
by means of at least one bolt 84. Slidable within the body
is a plunger 85 which has a central bore through which a
fixing screw 86 secures the die 53 at the outer end of the
plunger 85. The plunger is biassed to a retracted position
by means of a helical compression spring 87 between the
plunger and the flange 83. The inner face 88 of the plunger
is shaped to conform to a respective conical cam 90
(Figure 6).
The die 53 comprises a flanged bush 110 which is held within
the plunger 85 by means of the screw 86 and a die plate 111
secured to the flange of the bush 110 by rivets 112 (Figure
9) -
As mentioned previously, the tape 48 passes underneath the
guide 59. Around the die 53 the guide 59 has a window 113
defined by two tapered portions 114, 115 of the guide. This
window enables the web to be pressed AgAin~t the tape and
the die by the respective impression band or roller. In the
space under the tapering portions 114, 115 is a guide 116 in
the form of a bridge. This is apertured to accommodate the
die 53. The guide 116 serves to guide the tape from -the
passageway to a position approximately flush with the outer
WO90/14953 PCT/GB90/00759
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surface of the guide 59 so that the tape is close to the
paper and is guided as not to be fouled by the die. The
guide 116 is fixed to the floor of the slot 100 by a fixing
screw (not shown).
AS is shown in Figure 6, within the half shafts 68 and 69 is
a hollow shaft 91 which carries the conical cams 90, 90a and
90b. Each cam actuates a respective die or dies by
engagement with the face 88 of the respective plunger. The
shaft 91 is mounted for rotation on bearings 92, 92a and can
be moved axially by means of a spigot 93 which is operable
by a pneumatic assembly 94 of any suitable form.
The assembly 94 may be deactuated to allow the dies to
retract when cylinder rotation stops, because heated dies
need to be retracted when the cylinder is not rotating to
~rev~rlL heated dies being in continuous pressurized contact
with the web or the impression belt.
Heat for the dies may be provided by electrical heaters 95
each clamped to one of the conical cams, as shown for cam
90, the heaters being supplied with electrical current by
way of slip rings (not shown).
