Field of the Invention
This invention relates to the manufacture of security paper
and is particularly concerned with a method for producing coloured watermarks in
Background to the Invention
The watermark is an important feature in security papers
as a means for preventing counterfeiting of the final printed document. The reason
for the effectiveness of the watermark is that, as it is formed in the early stages
of manufacture, it is created as part of the paper structure and therefore cannot
be easily simulated in the illegal production of a false document.
It is believed that the introduction of colour into the
watermark would further enhance the effectiveness of the feature as an anti-counterfeit
device. It is accordingly an object of the present invention to provide a method
of manufacturing security paper that incorporates a coloured watermark.
The invention is concerned with watermarks of the tonal
type where the image is created by variations in fibre density, both light and dark,
and does not relate to the simple line-mark type that are completely light in appearance
in relation to the paper.
Tonal watermarks are created from impressions embossed
into woven wire-mesh and are generally referred to as "embossed".
There are two methods of producing watermarks in paper
based on the two methods of paper production, the fourdrinier and the cylinder mould.
Both processes are well established and relate to the method of forming the paper
structure. The technologies are well known and have been in use since the early
part of the 19th century. The fourdrinier forming process is by far the
most common, whilst the cylinder mould process finds a niche in specialist areas.
With the fourdrinier process, the watermark comes from
images embossed into a wire-mesh cover of a roll known as the dandy roll. In paper
manufacture, the dandy roll is in intimate contact with already formed paper web.
At the point of contact, the web is still in the wet state and the fibres are relatively
mobile. The action of the dandy is to partly reorganise the fibre structure in line
with the embossings on the surface of the dandy, thus creating an image of varying
density, which is visible in transmitted light when the paper web is subsequently
Unlike the fourdrinier method, which is based in the paper
web being formed on a flat table, the cylinder mould forms the web on the surface
of a wire-mesh covered cylinder, and the watermark image is embossed into wire-mesh
covering. It is clear, therefore, that in the case of the cylinder mould the watermark
is formed during the formation of the basic sheet, whereas with the fourdrinier,
the sheet is formed and at a critical point after this, fibres are moved into coincidence
with the embossed design on the dandy cover.
In both processes, there is generally no difference between
the fibres forming the watermarks and the fibres forming the main sheet structure.
This integral structure does not allow for a difference in fibre type or colour
for the watermark using conventional methods.
A specific object of the present invention is to provide
an alternative method for the production of high definition, watermarks.
The primary advantage of the method of the present invention
is to allow the manufacture of coloured watermarks, However, there are advantages
to be gained if the method of the present invention is used for non-coloured watermarks.
The term "coloured" implies a range of colouring from very light and subtle shades
to strong bright colours when viewed against the colour of the basic paper sheet.
It is further intended that the term "colour" also covers the colouring of the watermark
structure with optical brightening agents (OBA), thus allowing a visual difference
when viewed under ultra violet (u.v.) light, when the main sheet is u.v. dull.
Summary of the Invention
According to a first aspect of the present invention there
is provided a method of producing coloured watermarks that includes using a watermark
applicator to which auxiliary coloured stock is supplied.
The watermark applicator may be a former.
According to a second aspect of the present invention there
is provided a watermark applicator that includes a cylinder with an open structure
(similar to the open body of a dandy roll) and covered with an embossed wire mesh.
Discrete embossings are applied to the mesh, the areas
of the mesh within the embossings being permeable while the parts of the mesh between
the discrete embossings are rendered impermeable to water.
According to a third aspect of the present invention there
is provided a method of making security paper that includes the use of coloured
auxiliary stock and in which the coloured auxiliary stock is concentrated only on
the areas representing the watermark.
The watermark applicator cylinder may be in intimate contact
with the pre-formed moist sheet leaving the forming section of the fourdrinier or
cylinder mould. This, however, will not be the case for the open-draw fourdrinier
process, nor when a former is used as an applicator.
According to a fourth aspect of the present invention there
is provided a method of producing security paper that includes the use of concentrated
stock for forming a watermark and in which the concentrated stock representing the
watermark is transferred intact to the surface of a continuous paper web in discrete
units, to then be carried into the press section of the paper machine where it is
consolidated into the sheet structure by pressure and water removal.
In the method of the present invention, the watermark is
totally formed by the watermark applicator and transferred to the continuous paper
web after the fourdrinier and cylinder mould. As the watermark is formed solely
by the watermark applicator, un-embossed wire-mesh can be used to cover the mould
cylinder and the dandy roll. In this case, the dandy roll will be used solely to
improve sheet formation. As mentioned above, coloured watermarks can be useful in
providing additional security to a document against counterfeiting.
The production of non-coloured watermarks using the watermark
applicator of the present invention can also provide advantages as follows:-
Brief Description of the Drawings
- 1) On the cylinder mould, the requirement for the number of embossings is greatly
reduced giving savings in both time and cost.
- 2) The need to change the mould cover between different making orders is eliminated,
thus giving savings in production time.
- 3) On the fourdrinier machine, it will generally be possible to produce watermarks
of greater detail and clarity when compared with the dandy roll method of manufacture.
- 4) With the fourdrinier machine, it has been difficult to impart a watermark
using stock that is highly fibrillated to achieve maximum paper strength - as in
the case of currency paper. The method of the present invention enables clear watermarks
to be achieved by supplying suitable auxiliary stock to the watermark applicator.
Description of the Preferred Embodiments
- Figure 1 is a simplified sectional view of a cylinder mould forming unit with
the additional features of the present invention and with the first part of a press
- Figure 1A shows a modification of the arrangement shown in Figure 1, such modification
involving the introduction of a former adjacent the watermark applicator,
- Figure 1 B shows another modification of the arrangement shown in Figure 1,
such modification involving the use of a former to perform the function of the watermark
- Figure 2 illustrates the watermark applicator of Figure 1,
- Figure 3 is a sectional view of a suction pick-up from a fourdrinier forming
unit with the additional features of the present invention followed by the first
part of a press section, and
- Figure 3A is a sectional view of an open draw web transfer from a fourdrinier
forming unit with the additional features of the present invention followed by the
first part of a press section.
Figure 1 represents a section through a conventional cylinder
mould and the diameter is typically of the order of 1.4 metres. The plan view is
not shown but the operating width of each component in the diagram may be about
1.8 metres in actual size.
In the paper making operation by this method, the moist
web is transferred from the surface of the mould cylinder 1 by a couch roll 2 on
to a continuous porous fabric 3. Under conventional conditions, the porous fabric
3 carrying the continuous web will be carried to the press section 5 by idling rolls
represented by 4. From there it will continue on through further pressing and drying.
In the method of the present invention the watermarks are
not formed from the surface of the mould cylinder 1, as would normally be the case,
but by means of a watermark applicator represented by numbers 6, 7, and 8. Details
of the watermark applicator are shown in Figure 2.
Dilute fibrous paper stock is fed to the watermark applicator
at 10. This stock may be different from the main stock supplied to the mould cylinder
at 9 although this is not necessarily so. Similar stock at 10 to the main supply
at 9 would yield conventional watermarks. To obtain coloured watermarks, a different
fibre stock, referred to as auxiliary stock, is prepared using pre-dyed fibres.
This could be provided from repulped coloured or fluorescent papers. The auxiliary
stock is diluted and dispersed in a separate system 19, and then pumped (at a consistency
of about 0.3 to 0.9%) to the watermark applicator tray 7.
The cross-section of the watermark applicator is shown
in Figure 2. It consists of an applicator cylinder 6 with an open structure that
is covered by a wire-mesh. This cylinder is manufactured as would be a dandy roll.
Before the wire-mesh cover is fitted, it is first embossed in the required watermark
design, represented as 14. A significant feature of the method of the invention
is that the wire-mesh cover is treated so that the un-embossed land area is rendered
impermeable to the inflow of water. This may be achieved in a number of ways, e.g.
by coating with latex, lacquer or a plastic material or by shrinking on a sleeve
and exposing the embossings by "cut-outs". A stainless steel tray 7 receives the
auxiliary stock through 10. The level in the tray 7 may be controlled by an overflow
8 or by a level control system (not shown).
The applicator cylinder 6 is shown (see Figure 1) in intimate
contact with the continuous web supported by the porous fabric 3 backed by the light
pressure of a couch roll 15. This contact causes the applicator cylinder surface
to rotate at the speed of the continuous web. During this rotation, fibres from
the auxiliary stock are concentrated in the watermark embossings by the inflow of
water through the open mesh forming a moulded replication of the image. As the rotation
proceeds, the watermark replicas are transferred to the continuous web in step with
the spacing on the cylinder. They are then carried forward to the press section
5. Here, by pressure and water removal, the watermark replicas become completely
bonded into the paper.
Water must be continuously removed from the inside of the
applicator cylinder 6. This can be achieved by an open-end to the cylinder with
an appropriate sealing arrangement (not shown) or, as in Figure 2, by means of a
rotating joint carrying a siphon pipe 11 activated by a fan 12 and sealed by a drop-leg
13. The ends of the cylinder 6 are sealed.
It is common practice in many modern plant to introduce
a forming unit (or former) that is arranged to operate in tandem with the mould
cylinder. This arrangement is shown in Figure 1A, which illustrates the relative
positions of the former 21, the watermark applicator cylinder 6 and the mould cylinder
Figure 1 B shows an arrangement in which the former 21
performs the function of the watermark applicator of Figure 1. A stock supply header
22 receives auxiliary stock through a supply pipe 10 and the wire mesh covering
the cylinder of the former 21 is watermark-embossed, with the un-watermark areas
being blocked as described above. The watermark replicas are transferred directly
on to the transfer fabric 3 and this couching process is aided by the application
of a partial vacuum from a suction box 23. The watermark replicas are consolidated
into the main sheet structure at the nip of the couch roll.
The parts of the apparatus shown in Figures 1A and 1B that
correspond to the parts of the apparatus shown in Figure 1 are indicated by the
same reference numerals as those used in Figure 1.
Similar technology applies to the fourdrinier process.
As shown in Figure 3, the continuous web of paper is removed from the forming fabric
20 by means of a suction pick-up roll 16 and is carried forward by a continuous
porous fabric 3, normally to the press section 5. According to the method of the
present invention, the watermark applicator is interposed between the suction pick-up
16 and the first idling roller 4. The action of the watermark applicator is precisely
the same as for the cylinder mould process and delivers watermark replicas that
are taken to the press section 5 for consolidation into the paper web. The paper
web at 18 continues on to be dried in the normal way, and the final paper will contain
watermarks of the normal appearance or coloured, if coloured fibres are used in
the watermark applicator.
Figure 3A shows an open-draw fourdrinier forming unit in
which the web is transferred from the suction couch 16 to the press fabric 17 unsupported.
With this arrangement, the watermark replicas are created on the surface of the
applicator cylinder 6 in the manner described above, but they are then couched directly
on to the transfer fabric 3. They are then combined and consolidated into the continuous
paper web in the nip of the first press section 5. To aid the couching (transfer)
process from the watermark applicator to the fabric 3, an inverted suction box (not
shown) may be used either to replace the couch roll or in combination with the couch
The parts of the apparatus shown in Figures 3 and 3A that
correspond to the parts of the apparatus shown in Figure 1 are indicated by the
same reference numerals as those used in Figure 1.
In order to avoid difficulties in printing the security
paper with watermarks formed in accordance with the present invention, it is important
to avoid undue thickness above the un-watermarked areas of the sheet. To this end
it is advisable, firstly, to limit the embossing depths on the applicator wire mesh
to a maximum of the order of 1.0 mm. Secondly, in order to increase the apparent
density in the watermark areas, and thus selectively reduce the thickness in these
areas, it is advantageous to use a wet smoothing press (an offset press) immediately
following the (wet) press section.