[0001] The present invention relates to a watermark formation element for forming watermarks
in paper, a cylinder mould cover comprising such a watermark formation element, a
method of making such a cylinder mould cover, a method of making paper using such
a cylinder mould cover and paper made thereby.
[0002] The use of watermarks is fairly common in many security documents. High security
multi-tonal watermarks are typically created using a cylinder mould process and these
are commonly known as cylinder mould watermarks. Cylinder mould watermarks are formed
by varying the density of paper fibres so that in some regions the fibres are denser,
and in others less dense, than that of the base paper layer which surrounds and separates
the denser and less dense regions. When viewed in transmitted light the less dense
regions are lighter and the denser regions darker than the base paper and the contrasts
can be seen very clearly. Different types of watermarks have different advantages.
A cylinder mould watermark, usually formed on an embossed cylinder mould cover, is
often a pictorial image, such as a portrait, and can be very detailed and complex
which significantly reduces the risk of counterfeiting.
[0003] In cylinder mould papermaking, paper is formed on a partially submerged wire cloth
covered mould cylinder, which rotates in a vat containing slurry comprising a dilute
suspension of paper fibres. As the mould cylinder rotates, water is drawn through
the wire cloth depositing fibres onto the cylinder surface. When the wire cloth of
the cylinder mould cover is embossed, the fibres deposit with a lesser or greater
thickness on the raised and sunken elements respectively of the embossing to form
a three-dimensional watermark in the finished paper.
[0004] The variation in paper thickness in the final watermark is a result of fibre movement
from the raised regions of the embossed mesh to the sunken regions of the embossed
mesh as the water is drawn through the wire cloth. The fibre movement, and therefore
the tonal variation in the watermark, is governed by the drainage rate and that is
dependent on the profile of the embossing. This enables excellent control in the gradation
of the watermark pattern, producing a subtle tonal range that is unique to the embossed
cylinder mould watermark process.
[0005] Traditional embossed cylinder mould watermarks have to be made within the constraints
imposed by the physical properties of the wire cloth. Embossing the wire cloth of
the cylinder mould cover reduces its strength and increases the risk of damage to
the mould cover and the paper during the papermaking process. This is particularly
the case if there is a sharp transition from a deep area of embossing to a significantly
raised area. Furthermore, within a complex pictorial watermark it is difficult to
juxtapose a very light tone next to a very dark tone due to the stresses that this
would place on the mould cover itself during embossing. The limit on the "verticality"
of a sidewall within an embossing is approximately 70% to avoid these problems. However
the more vertical the side wall, the sharper the image as there is a greater contrast
between a light and dark area. One way around these problems to is use an overcut
on the embossing die, which provides the space for the deformation of the wire cloth.
However it is often very difficult to adjust the watermark image to provide such overcuts.
[0006] The watermark image resolution is also constrained by the coarseness of the mesh
of the wire cloth. Furthermore, the wire cloth superimposes a mark on the paper as
a consequence of it being a woven structure. This may also detract from the resolution
and clarity of the watermark image.
[0007] Some of these constraints can be reduced by using a finer wire, but this leads to
reduced mould cover durability as finer wires wear out faster.
[0008] It is also very difficult to produce light watermark regions exhibiting a significant
surface area using the embossed cylinder mould technique.
[0009] An alternative process for generating uniform light tonal regions (and providing
enhanced watermark security) is the electrotype process. In the electrotype process
a thin piece of metal, generally in the form of an image or letter, is applied to
the wire cloth of the cylinder mould cover, usually by sewing or welding. The electrotype
creates a significant decrease in drainage and fibre deposition and thereby forms
a light watermark in the paper. An electrotype watermark produced in this manner may
be lighter than the lightest areas of an embossed cylinder mould watermark. The electrotyping
process is well known in papermaking and has been described, for example, in
US-B-1901049 and
US-B-2009185.
[0010] An electrotype watermark is therefore an area of paper having just a uniform decrease
in paper thickness. The area is typically quite small and the change in paper thickness
(fibre density) is quite distinct so as to create very light areas. The electrotype
process is limited in that, if the electrotype is too large, this can produce a hole
in the paper. The typical width of the electrotype is between 0.2 to 1.2mm and the
thickness is between 500 and 700µm, to avoid such problems.
[0011] Both of the aforementioned types of watermark have security (anti-counterfeiting)
benefits and have provided the backbone of paper security for hundreds of years. However,
both can be compromised and, as with all security devices, there is a need to improve
them. One approach is to provide ever more complex and technically demanding designs.
[0012] Such complex designs may require the combination of both embossed cylinder mould
and electrotype watermarks, or watermark areas, in the same design. For example electrotypes
have been used to produce very light highlights within an embossed cylinder mould
watermark. One such example is a watermark in the form of the head of an animal, in
which the bright eyes of the lion are electrotype watermarks. In transmission the
eyes will appear significantly brighter than the parts of the watermark produced by
the embossing and will therefore provide a level of contrast not usually achievable
by an embossed watermark alone.
[0013] One problem with integrating an electrotype watermark into an embossed cylinder mould
watermark lies in the difficulty in attaching the electrotype to the undulating embossed
region of the wire cloth of the cylinder mould. The specific area to which the electrotype
is attached must be flat, which of course is problematic within an undulating structure.
However the process for placing an electrotype within the embossed region of the wire
cloth is very difficult. A reinforced platform, or other form of support, is usually
required whilst the electrotype is being welded to the wire cloth, to prevent deformation
of the wire cloth, and therefore the embossing. Any deformation can lead to the watermark
design being compromised. However, it is often the case that it is difficult to provide
the appropriate support due to the nature of the embossing.
[0014] The addition of an electrotype to an embossed cylinder mould cover is also a time
consuming process. This increases the time to produce the cylinder mould cover for
production, and the cost thereof. The process for producing cylinder mould covers
for embossed cylinder mould watermarks is already lengthy. Once the art work is created,
this has to be converted into a program which operates a milling machine to produce
the embossing dies. The embossing dies are then used to emboss the wire mesh.
[0015] As an alternative to using electrotypes for producing highlights in a cylinder mould
watermark, it is possible to close the mesh openings in certain areas to prevent drainage.
However this does not create the sharpness of contrast which is possible with electrotypes.
[0016] A cylinder mould machine is generally used to manufacture one or more webs of paper.
The web is subsequently slit into interim sheets of paper and then usually further
slit into smaller sheets for making documents. The length of the cylinder mould cover,
on which the paper is formed, is determined by the number of webs to be produced,
where the width of each web corresponds to the width of one interim sheet. Typically
the length will be such as to produce three webs. The circumference of the cylinder
mould cover is equivalent to the length of a number of interim sheets. As a non-limiting
example, there may be three webs and six interim sheets, so the surface area of the
cylinder mould cover would corresponding to the surface area of 18 (3 x 6) interim
sheets. As each interim sheet is subsequently slit into a plurality of smaller security
documents, the number of watermarks produced in each interim sheet must be such as
to produce the requisite watermarks in each of the finished documents. A typical mould
cover may therefore have embossings/electrotypes for around 700 documents.
[0017] However, it may be convenient for each of the webs to have different watermarks.
This enables the production in a single manufacturing run of, for example, all the
pages for a passport which have different watermarks on each page. The requirement
for different watermarks on different webs adds complications to the manufacture of
the cylinder mould cover, because of the difficulty of placing them robotically. This
also significantly adds to the cost, because of the cost of making individual dies
or electrotypes for each variant.
[0018] In order to maximise the difference between the light and dark areas of a watermark
formed by the profiled surface of the embossings, it is desirable to control the drainage
in both the raised and sunken areas of the embossing. This is currently achieved in
the raised areas by reducing the drainage rate (i.e. the rate at which water passes
through the wire cloth during the forming process), typically by placing an impermeable
element, such as a metal plate or plastic element, beneath the innermost layer of
the wire cloth. The weave structure of the wire cloth still allows water to drain
laterally there through, albeit at a reduced rate. However radial drainage is blocked
by the impermeable element.
[0019] In the sunken areas, control is achieved by increasing the overall drainage rate,
for example by applying a vacuum to the cylinder mould, or by starting the draining
process below the stock level, for example by using a mould curtain. Another method
is to increase the embossing depth of the forming surface. This, however, makes the
mould cover more vulnerable to damage and can result in difficulties releasing the
partially formed paper onto the felt (formex) which transports the paper from the
wet end of the papermaking machine to the press section.
[0020] Neither of these solutions is very effective. Underwire drainage restriction is limited
by the lateral drainage resulting from the 3-dimensional structure of the wire cloth.
The application of vacuum and the mould curtain both affect the raised and sunken
areas simultaneously, making them coarse tools for selective drainage control.
[0021] US-A-2010/0175843 and
US-A-2013/0092337 propose an alternative method of producing multi-tonal watermarks. In this method,
instead of embossing the cylinder mould cover, a perforated watermark "insert" is
attached to the cylinder mould cover which provides a multi-level relief. The insert
may be injection moulded to provide the profiled surface perforations. Alternatively
the insert is deep drawn or hot stamped.
[0022] US-A-2013/0255896 also proposes an alternative method of producing multi-tonal watermarks. In this
method, a "part" is attached to the cylinder mould cover, which part has a profiled
surface and conical perforations extending from the profiled surface to an opposing
drainage surface. The part is made by a laser sintering method, such as SLM or SLS.
[0023] There is, however, always a need to improve the watermarking process. One object
is to improve the quality of watermarks and in particular to improve the ability to
create the effects produced currently by embossed cylinder mould and electrotype watermarks,
so that complex multitonal designs or images can be created with sharply contrasting
dark and very light areas adjacent each other.
[0024] Another object is to provide a process for the production of cylinder mould covers
which enables each watermark, or some watermarks, to be individually modified.
[0025] Yet another object is to improve the process for the production of cylinder mould
covers by decreasing the time taken from the production of the art work to the completion
of the mould cover.
[0026] A further object is to reduce the cost of production of cylinder mould covers by
simplifying the manufacturing process, whilst retaining the ability to produce complex
multi-tonal designs or images with sharply contrasting dark and very light areas adjacent
each other from the resulting cylinder mould cover.
[0027] A further object still is to reduce the cost of production of cylinder mould covers
by utilising a process which enables cheaper materials to be used and to reduce material
wastage.
[0028] The invention therefore provides a watermark formation element for forming at least
one watermark in a paper, said watermark formation element having an integrated body
comprising a watermark forming surface, which has one or more watermark forming regions,
and a drainage surface, said watermark formation element having a plurality of drainage
channels extending from front surface apertures in the watermark forming surface to
the drainage surface, said watermark formation element further comprising integral
means for fixing the watermark formation element to a wire mesh of a cylinder mould
cover
[0029] The integral fixing means is preferably porous and/or has an internal drainage passage
there through.
[0030] The integral fixing means may comprise at least one tubular spigot which extends
from the drainage surface, the spigot having an internal drainage passage and at least
one barb located on its distal end.
[0031] Alternatively the integral fixing means may comprise at least one flexible wire which
extends from the drainage surface.
[0032] The watermark formation element is preferably formed from a plurality of layers,
each layer being provided with drainage apertures, the drainage apertures in each
layer at least partially overlap the drainage apertures in any adjacent layers to
form said drainage channels.
[0033] Each layer may be formed from a plurality of sub layers.
[0034] The layers and/or sub layers are preferably fused together to form the integrated
body.
[0035] In a preferred embodiment, the watermark formation element is formed by 3D printing.
[0036] The watermark formation element is preferably formed from a polymeric material or
a plurality of different polymer materials or from a metallic material or a plurality
of different metallic materials.
[0037] Preferably the minimum cross-sectional area of the front surface aperture and of
any section of the drainage channels is 0.01mm
2.
[0038] The shape of the drainage apertures in different layers may be different.
[0039] Preferably any one layer may have drainage apertures, the cross sectional area and/or
shape of are not all the same.
[0040] In a preferred embodiment the total cross sectional area of the front surface apertures
lies in the range of 1% to 40% of the total surface area of the watermark formation
element, preferably 15% to 30% and more preferably 15% to 25%.
[0041] The layers may be planar or non-planar.
[0042] Preferably the watermark formation surface is contoured in the one or more watermark
forming regions to provide tonal variation in the paper formed thereon.
[0043] The shape, size, spacing and or distribution of the drainage surface apertures may
be varied within the one or more watermark forming regions to provide tonal variation
in the paper formed thereon.
[0044] The invention further provides a cylinder mould cover for manufacturing a paper having
at least one watermark, comprising at least one foraminous layer and at least one
watermark formation element attached thereto by sais integral fixing means.
[0045] The watermark formation element may be located in a recess formed in the at least
one foraminous layer or in a cut out portion formed in the at least one foraminous
layer.
[0046] Alternatively the watermark formation element is located in a recess formed in the
at least one foraminous layer and a cut out portion formed in another foraminous layer.
[0047] The invention further provides a method of making the cylinder mould cover wherein
the one or more watermark formation elements are formed by a 3D printing process.
[0048] Preferably the one or more watermark formation elements are formed and subsequently
attached to the least one foraminous layer.
[0049] Alternatively the one or more watermark formation elements are formed directly on
the at least one foraminous layer.
[0050] The invention further provides a method of making watermarked paper comprising the
step of depositing fibres on the cylinder mould cover.
[0051] The invention further provides paper formed by this method.
[0052] The invention further provides a secure document made from this paper comprising
a banknote, a passport, a certificate, a ticket or the like.
[0053] Watermark formation elements and elements thereof, cylinder mould covers and methods
of making cylinder mould covers, watermark formation elements and paper will now be
described, by way of example only, with reference to the accompanying drawings, in
which:-
Figure 1 is cross section of a section of a wire cloth used to form a cylinder mould
cover;
Figures 2a and 2b are plan views of different watermark formation elements;
Figure 3a is a cross sectional side elevation of the watermark formation element of
Figure 2a on the line III-III;
Figures 3b to 3d are cross sectional side elevations of the watermark formation element
of Figure 2b;
Figure 4 is a plan view of a front surface aperture in the watermark formation surface
of the watermark formation element of Figure 2;
Figures 5a and 5b are cross sectional elevations through an adjacent pair of two different
aperture defining members defining the front surface aperture of Figure 4 on the line
V-V;
Figures 6a to 6e illustrate the construction of an alternative watermark formation
element;
Figures 7a to 7d illustrate the construction of a further alternative watermark formation
element;
Figures 8 to 17 are cross sectional side elevations of yet further alternative watermark
formation elements attached to the wire cloth of a cylinder mould cover;
Figure 18 is a plan view of a single watermark formation element;
Figure 19 is a tessellated sheet section made up of the watermark formation elements
of Figure 18;
Figure 20 is a single watermark formation element used to produce multiple documents
having identical watermarks
Figures 21 to 24 and 26 to 28 are parts of different watermark formation surfaces
of different watermark formation elements
Figure 25 is a further alternative watermark formation element; and
Figures 29 to 32 are perspective views showing how adjacent sheets of watermark formation
elements can be joined together.
[0054] It should be noted that, whilst the following description specifically refers to
making paper, this should be interpreted as referring to paper made from any fibrous
substrate, whether made from natural and/or synthetic fibres.
[0055] Watermarked paper is usually formed on a partially submerged cylinder mould cover,
at the wet end of a papermaking machine, as it rotates in a vat containing paper slurry.
The paper slurry generally comprises an aqueous suspension of paper fibres, which
maybe natural fibres, synthetic fibres or a combination of both. As the cylinder mould
rotates, liquid is drawn through the wire cloth 10 depositing fibres onto the face
cloth 11.
[0056] A typical prior art cylinder mould cover is formed from a multi-layered wire cloth
10, as shown in Figure 1. The layers are usually made from wire mesh or another foraminous
surface. The outermost layer (when the wire cloth 10 is wrapped around the cylinder
mould) is known as the face cloth 11 and the next layer is a backing layer, referred
to herein as the first backing layer 12. The face cloth 11 and first backing layer
12 are the layers which are usually provided with embossings 13 which form the watermarks.
Behind these layers 11,12 is usually a second backing layer 14, which typically has
cut-out areas 15 which accommodate the inwardly projecting areas of the embossings
13. The innermost layer (when the wire cloth 10 is wrapped around the cylinder mould)
is usually a third backing layer 16 which is not embossed or cut out, which provides
overall support and strength to the overlying layers 11,12,14. Typically the face
cloth 11 has the smallest mesh openings, with the third backing (innermost) layer
16 having the largest mesh openings.
[0057] To form electrotype watermarks, electrotypes 17 may be attached to the face cloth
11 by a suitable method, such as welding or soldering.
[0058] For some types of embossings 13, supporting elements 18 may be inserted between the
rearmost embossed layer, in this example first backing layer 12, and the next adjacent
layer, in this example the third backing layer 16. The supporting elements 18 are
typically made from stainless steel with holes drilled therein to provide drainage.
These supporting elements 18 do not provide drainage restriction in the way that electrotypes
17 do, but are provided to help prevent distortion of the embossings 13 when the mould
cover is subjected to pressure during the papermaking process.
[0059] As an alternative to using the embossings 13 and/or electrotypes 17 of the prior
art, watermarks may be formed using watermark formation elements 20. At least one
watermark formation element 20 is preferably attached to the wire cloth 10 of the
cylinder mould cover. It should be noted that the wire cloth 10 may have a similar
construction to that of Figure 1, in terms of the number of layers 11,12,14,16, or
it may have a different number of layers. The watermark formation element 20 has a
watermark forming surface 21. At least a part of the watermark forming surface 21
may have a contoured profile, like the surface of a watermark embossing 13, which
provide one or more watermark forming sections 52. The fibres deposit with a lesser
or greater thickness on the raised and sunken elements of the watermark forming section(s)
52 to form a 3-dimensional watermark in the finished paper. The watermark forming
surface 21 may also have non-contoured sections (non-watermark forming sections) on
which paper is produced which has no watermarks. However, the deposition of fibres
to form watermarks may be controlled by additional and/or alternative means, for example
by varying the drainage rate of the liquid from the paper slurry through the watermark
formation element. These means are described below.
[0060] The watermark formation element 20 has an integrated body (i.e. one not comprising
discernible separate layers) a plurality of drainage channels 22 extending from front
surface apertures 23 in the watermark forming surface 21 to drainage surface apertures
24 in an opposing drainage surface 25 (see Figures 3a to 3d). The drainage channels
22 are not just located in the watermark forming sections 52, but also in the non-watermark
forming sections. The drainage channels 22 allow liquid from the paper slurry to drain
through the watermark formation element 20 to enable the fibres to deposit on the
watermark forming surface 21. The cross sectional area of each drainage channel 22
preferably increases as it extends from the watermark forming surface 21 to the drainage
surface 25 to encourage the flow of liquid (as shown in Figures 6a to 6e). Preferably
the minimum cross sectional area of the front surface apertures 23 and of any section
of the drainage channels 22 is 0.01mm
2. However, the cross sectional area of one or more drainage channels 22 may remain
constant as it extends from the watermark forming surface 21 to the drainage surface
25, or it may decrease.
[0061] Each of the front surface apertures 23 preferably has a curved rim 26 which extends
from the watermark formation surface 21 to an inner wall 29 of the drainage channel
22. The radius of curvature (r) of the rim 26 is selected to reduce fibre retention
as the liquid drains through the watermark formation element 20 and to help in the
cleaning of the watermark formation element 20. The rim 26 preferably has a radius
of curvature (r) (see Figures 5a and 5b) in the range of 0.05 to 0.25mm, and more
preferably in the range of 0.1 to 0.15mm.
[0062] The continuous flow of liquid through the drainage channels 22 is important, as blockages
can lead to imperfections in the watermark. The size, number, cross-sectional shape
and/or profile of the drainage channels 22 are preferably selected to provide controlled
drainage rates in different areas to form the desired watermark(s). Thus, the watermark
formation element(s) 20 and cylinder mould cover provide a forming surface with variable
porosity, such that areas with lower porosity produce reduced grammage (i.e. lighter
areas with a lower density of fibres) areas in the paper, and areas with higher porosity
enable higher grammage areas (i.e. darker areas with a higher density of fibres) to
be produced.
[0063] From Figures 3a to 3d it can be seen that some of the drainage channels 22 may be
longer than others as a result in a varying profile of the watermark forming surface
21. The longer drainage channels 20 provide more resistance to the flow of liquid
flow than the shorter drainage channels 20 and therefore produce lighter areas in
the paper than those produced by the shorter drainage channels 20. Variations in paper
density may thus be controlled not only by the variations in the profile of the watermark
forming surface 21, but also (alternatively or in addition) by the rate of liquid
flow through the drainage channels 22.
[0064] Between the front surface apertures 23, the watermark formation surface 21 comprises
solid areas 27. These solid areas 27 further enable the control of deposition of fibres
on the watermark formation surface 21. These solid areas 27 may be regular and small
or may be used, by varying their size and position, to create the equivalent of electrotype
watermarks, i.e. significantly brighter/lighter areas. The fibre deposition on each
solid area 27 is a function of the width of the solid area 27 (i.e. the distance between
adjacent front surface apertures 23) and the height of solid area 27 relative to adjacent
portions of the watermark forming surface 21. In order to produce a watermark, the
preferred maximum width of a solid area 27 is approximately 2mm; otherwise the fibres
are unable to bridge the solid area 21 which would result in a hole in the paper.
However, if it is desirable to create a hole in the paper, the solid areas 27 may
be bigger.
[0065] The solid areas 27 may be rounded (as shown in Figure 5a) or flat (as shown in Figure
5b). Where the watermark forming surface 21 has a variable profile, which has peaks
(where fibres are less densely deposited) and troughs (where fibres are more densely
deposited), the solid areas 27 may be located within the peaks or the troughs, having
differing effects. Thus a peak alone would produce a light area, and a high solid
area 27 located within the peak would produce an even lighter area. A trough alone
would produce a dark area, and a high solid area 27 located within the trough would
produce a very bright high light directly adjacent to, or completely surrounded by,
a dark area.
[0066] The solid areas 27 of the watermark formation element 20 may form a regular pattern,
for example the mesh like pattern as shown in Figures 2a and 2b. They may also form
larger areas, for example the areas marked with reference numeral 28 in Figure 2b.
These larger solid areas 28 can be formed in a number of different ways, some examples
of which are shown in Figures 3b-3d. In the example illustrated in Figure 3b the larger
solid areas 28 extend over, and block off, a number of drainage channels 22. In the
examples illustrated in Figures 3c and 3d the larger solid areas 28 extend from the
watermark formation surface 21 to the drainage surface 25. In the examples illustrated
in Figure 3b and 3c one of the larger solid areas 28 has a variable profile, in this
case a stepped profile, whereas the other has a flat surface.
[0067] The larger solid areas 28 between the drainage surface apertures 24 preferably have
a cross sectional area of at least three times that of the drainage surface apertures
24.
[0068] The front surface apertures 24 define a shape, and the shape defined by the front
surface apertures 24 may be different from one set of front surface apertures 24 to
another. The shape may be a geometric shape, such as a rectangle. Alternatively the
shape may be a circle, hexagon or another geometric shape. As a further alternative
they may define a non-geometric shape. The shape defined by the front surface apertures
24 may be regular or irregular.
[0069] The shape defined by the front surface apertures 24 may be in the form of at least
one alphanumeric, a pictorial image or a symbol. In the example illustrated in Figure
22, the front surface apertures 24 themselves are in the shape of an apple. In Figures
23 and 24 the front surface apertures 24 are in the form of text, in this example
the letters TNW. Preferably the watermark formation element 20 has front surface apertures
24 which define at least two different shapes. In these examples the front surface
apertures 24 define the shapes positively. However they may alternatively define the
shapes negatively, so that the solid areas 27 between the front surface apertures
24 have the aforementioned shapes. As mentioned above, some of the drainage surface
apertures 24 may define the shapes negatively and some may define them positively.
[0070] Where the front surface apertures 24 define alphanumerics, the stem width of the
character (where it acts a front surface aperture 24) is preferably no thinner than
0.3mm in width and the space between the characters (the solid areas 27 between the
front surface apertures 24) is preferably no smaller than 0.3mm. The minimum and maximum
character size used for the front surface apertures 24 may also be determined by the
style of the type face. It should also be noted that, although a minimum front surface
aperture 24/stem width size of 0.3mm may be intended, during the manufacturing process,
these dimensions may vary depending on the structure of the model, material and the
tolerance of the machine used to manufacture the watermark formation element.
[0071] The watermark formation element 20 may have one set of front surface apertures 23
which define one shape, and another set of front surface apertures 23 which define
a different shape. The first set may be located within the second set.
[0072] In these examples, where the shape of the drainage surface apertures 24 define a
particular shape or set of shapes, the watermark formation surface 21 in the watermark
forming section 52 does not need to be contoured, although it may be.
[0073] In addition to selecting a particular shape of the front surface apertures 24, the
watermark formation element 20 may be of a particular shape. For example, as shown
on Figure 25, the watermark formation element 20 has the shape of an apple. The shape
of the front surface apertures 24, the shape of the watermark formation element 20
and/or the watermark formed may also be selected to be the same as, or related in
context to each other. Thus in the example or Figure 25, the drainage surface apertures
24 and the watermark formation element 20 are in the form of apples, whilst the watermark
is a portrait of Sir Isaac Newton. Other shapes related in context could include an
emblem or geographical outline of a country and the letters indicating its currency;
the nature of a currency and numerals indicating its value; the geographical outline
of a country and images from its flag, e.g. Ghana and star, Sri Lanka and lion with
sword, Pakistan and crescent moon; portraits and quotations or identifying symbols,
e.g. Churchill and the phrase "fight them on the beaches", Lincoln and extract from
the Gettysburg address, Washington or Franklin and declaration of independence, Jane
Austen and quill pen. The shape of the watermark formation element 20 may be a symbol,
a pictorial image, an alphanumeric or a geometric or non-geometric shape. In this
example a first watermark forming section 52a forms a pictorial watermark having light
and dark shades, in the form of a head. The watermark formation element 20 may have
a border provided by larger solid areas 28. These may provide a suitable means of
anchoring the watermark formation element 20 to the face cloth 11. A second watermark
forming section 52b is provided which forms an electrotype type of watermark in the
shape of an apple which has just light shades.
[0074] Where such a shaped watermark formation element 20 is attached to the face cloth
11 of a cylinder mould cover, the finished paper manufactured thereon may have two
different "wire marks". When a web of substrate is formed using a cylinder mould cover,
the profile of the mesh of the face cloth 11 produces what is known as a "wire mark"
across the entire web. Generally, where the warp wires (in the machine direction)
and weft wires (in the cross direction) cross, a knuckle is formed which is slightly
raised relative to the warp and weft wires. The knuckles cause a very minor variation
in the density of the substrate fibres which are deposited on the surface of the mould
cover. The imprint of the face cloth 11 also causes a barely perceptible undulation
of the surface of the finished substrate and a regular pattern throughout the substrate
which is virtually indistinguishable to the unaided eye. Where a watermark formation
element 20 is attached to the face cloth 11, The finished paper will have one wire
mark formed by the mesh of the face cloth 11 and another formed by any regular pattern
formed by front surface apertures 23 and solid areas 27 watermark formation element
20.
[0075] As mentioned briefly above, the drainage rate can be controlled by a number of different
means (either alone or in combination) and this can be used to provide tonal variation
within the watermark(s). The size and/or shape of the drainage surface apertures may
be varied in a given horizontal plane, which is parallel to the drainage surface 25,
to achieve this. Some examples of watermark formation elements 20 used to form a watermark
in the form of a portrait are illustrated in Figures 28a and 28b. The watermark formation
surface 21 in each of these examples does not have to be contoured (although it may
also be contoured) as the size of the drainage surface apertures 24 varies to provide
the tonal variation. In these examples the drainage surface apertures 24 have the
same circular shape, although the shape may be varied. The size of the solid areas
27 between the drainage surface apertures 24 also therefore varies.
[0076] The drainage surface apertures 24 may positively define a shape (such as the circle
in Figures 28a and 28b) or they may negatively define a shape (so that the solid areas
27 therebetween positively have that shape). Alternatively the watermark forming section
52 may have drainage surface apertures 24 some of which positively define a shape
and some of which negatively define the same shape.
[0077] In the example illustrated in Figure 28, the drainage surface apertures 24 have a
circular shape. However a tonal variation can be achieved by varying the shape and/or
size of symbols, pictorial images or alphanumeric shapes. For example in the case
of the drainage surface apertures 28 having a shape of a letter, then the areas of
the watermark formation element 20 which form the darker regions in the final halftone
image in the watermark would have a larger stem width than the drainage surface apertures
24 forming the lighter part of the halftone image.
[0078] The spacing between the front surface apertures 24 in a given horizontal plane, which
is parallel to the drainage surface 25, can also be varied to provide tonal variation.
This again can avoid the need for the watermark formation surface 21 to be contoured
(although it could also be). Thus in the finished paper, the areas formed by the regions
of the watermark formation element 20 in which closer spaced front surface apertures
24 are located are darker than the areas formed by the areas in which the front surface
apertures 24 are more widely spaced. In the example illustrated in Figure 25, there
is a central band X in which the front surface apertures 24 are closer together than
those lying on either side of the band X.
[0079] Such watermark formation elements 20 can be used to provide a continuous variation
in the tone of the watermark from one section (preferably an end or an edge) thereof,
which has the lightest tone, to an opposing section (preferably the other end or opposing
edge), which has the darkest tone. This can be achieved using any of the aforementioned
methods of carrying the tone, such as by varying the height/depth of at least one
watermark forming section 52 of the watermark formation surface 21 or by varying the
apertures or a combination of both. One example of this feature is illustrated in
Figure 26. In this example, the watermark forming section 52 is configured to produce
at least one watermark in the finished paper which is a continuous spiral and has
a continuous tonal graduation from one end of the spiral, which is the darkest region,
to the other end, which is the lightest region. The light end of the spiral is produced
by larger solid areas 28 which are raised relative to the "normal" level (i.e. that
of the non-watermarking sections of the watermark formation surface 21), gradually
reducing in height at a continuous rate until the normal level of the watermark formation
surface 21 is reached, i.e. the level of the non-watermark forming sections. This
is marked as point A on Figure 26. At this point the watermark forming surface 21
starts to drop below the normal level, forming a channel 60 which increases in depth
at a continuous rate. The deepest end of the channel (i.e. at the other end of the
spiral) produces the darkest region of the spiral.
[0080] Such watermark(s) which has (have) a continuous tonal variation are preferably in
the form of a continuous line or band which may be straight, curved and which may
change direction e.g. a single straight line, an arc, a spiral, a zig-zag or the like
and which clearly have opposing ends. Such a watermark can provide a convenient method
of checking for counterfeits in that it comprises all multi-tones from light to dark
within a single watermark in a continuous graduation.
[0081] In one example, the preferred grammage of the finished paper in the darkest region
of the watermark is at least 140% of the grammage of the non-watermark regions. Thus
in one preferred example for 100 gsm background paper this would be approximately
140 gsm, and for 90 gsm background paper it would be approximately 126 gsm. However
these regions could have a heavier grammage still, preferably at least 160%, or more
preferably at least 180%, of the grammage in the non-watermarked regions. The lightest
region of the watermark, the grammage is preferably no more than 50% of the grammage
in the non-watermarked regions, more preferably no more than 40% and more preferably
still no more than 25%. Thus in one preferred example for 90 gsm background paper,
the grammage in the lightest region is 20gsm.
[0082] Thus for a 90gsm paper the grammage may range from approximately 20gsm to up to approximately
200gsm.
[0083] One technique for measuring grammage is as follows. A radiograph is generated by
exposing a sample sheet to a beta ray source (C-14) and recording the radiation transmitted
through the sheet on an X-ray film. The developed film is scanned with a flat-bed
scanner, and the grey levels of the image are transformed to actual grammage values
through a calibration scale obtained from a sample of known grammage.
[0084] The watermark formation element 20 may also be configured to produce such a continuously
graduated watermark located adjacent another watermark, which provides another convenient
anti-counterfeit check. The continuously graduated watermark provides a reference
chart, in that its darkest end matches the darkest regions in the adjacent watermark,
and the lightest end matches its lightest regions. The continuously graduated watermark
also has the colour of the base paper in the middle.
[0085] The watermark formation element 20 may also be configured to produce such a continuously
graduated watermark which blends into another watermark. In the example shown in Figure
27, in one area of the watermark formation element 20, a first watermark forming section
52a produces corner reinforcing watermarks of the type known from
EP-A-1468142, which has just darker shades formed by channels 60 having a constant depth. A second
watermark forming section 52b is formed adjacent the first watermark forming section
52a, which is configured to provide a continuous tonal graduation from the end of
the channels 60 to a pictorial watermark in a third watermark forming section 52c.
[0086] The watermark formation element 20 may also be configured to produce such a continuously
graduated watermark which has text or patterns within the continuous band or line.
These may be darker and/or lighter regions.
[0087] The watermark formation element 20 may be formed from a plurality of separate layers,
especially if formed using a 3D printing process as described below. However in the
finished watermark formation element 20 these layers may be integrally fused together
and indistinguishable as separate layers. The layers are formed with apertures, which
combine to form the drainage channels 22. The apertures in the top layer(s), which
form the watermarking forming surface 21, preferably have a smaller cross sectional
area than those in the bottom layer(s), which form the drainage surface 25. However
they may alternatively have a larger cross sectional area or the same cross sectional
area.
[0088] In one example, as shown in Figures 6a to 6e, there are pluralities of first layers
30, second layers 31, third layers 32 and fourth layers 33. Each of the first layers
30 are provided with apertures of one size, which form the front surface apertures
23. Each of the second layers 31 are provided with apertures 34 which have a larger
cross sectional area than the front surface apertures 23. Each of the third layers
31 are provided with apertures 35 which have a larger cross sectional area than the
apertures 34 in the second layers 31. Each of the fourth layers 31 are provided with
apertures which have a larger cross sectional area than the apertures 35 and which
form the drainage surface apertures 24.
[0089] Although the illustrated example shows four of each of the four layers 30,31,32,33,
the number of layers forming the watermark formation element 20 is not restricted
and the number of identical layers may also vary.
[0090] The apertures 23,34,35,24 in the different layers may have the same cross sectional
shape as each other, albeit with different cross sectional areas or the shape may
be varied from layer to layer.
[0091] The cross sectional area of the apertures 23,34,35,24 in any one layer may also be
varied, with larger apertures 23,34,35,24 providing increased drainage and fibre deposition
over smaller apertures 23,34,35,24.
[0092] The total cross sectional area of the front surface apertures 23 is preferably between
1% and 40% of the total surface area of the watermark formation element 20, more preferably
between 5% and 30%, and more preferably still between 15% and 25%.
[0093] The layers 30,31,32,33 illustrated in figures 6a-6d and 7a-7d are shown as planar.
However the layers may be non-planar, for example curved in one or more directions.
[0094] The drainage rate through the watermark formation elements 20 can additionally be
controlled by the open area and mean open diameter of the openings in the wire cloth
10 (or other foraminous surface), which provides the supporting structure. The mean
diameter of the openings is preferably between 0.02 and 0.4 mm and more preferably
between 0.05 and 0.1mm. The wire cloth 10 (or other foraminous surface) is preferably
produced by a method that is not constrained by the rate of change of gradient of
the watermark forming surface 21. This enables improved resolution and contrast to
be archived.
[0095] The drainage rate through the watermark formation elements 20 can further be controlled
by spraying, coating or otherwise covering the watermark formation surface 21 with
a material which changes the hydrophobic property of the material from which the watermark
formation element 20 is made. The hydrophobicity can be controlled by printing the
watermark formation element 20 with two or more different materials with different,
possibly widely varying, hydrophilic or hydrophobic natures which have different surface
energies/contact angles. For instance, if the wax support material (hydrophobic, non
wetting) is not fully removed from the 3D printed element, then water does not drain
readily through some drainage channels 22. This is because the contact angle of the
water droplet is too great and the droplet that forms will not pass through the drainage
channels 22. As a result, fibre is not deposited in that area to the same extent as
more hydrophilic areas and a highlight ensues. Thus if two constructional polymers
are used to form different areas of the watermark formation element 20, one more hydrophobic
than the other, although the size of the drainage channel 22 may be uniform across
the area, where a hydrophobic material is used then less fibre will be deposited and
so the image density can be modulated.
[0096] Equally it may be possible to adjust the drainage in some areas by coating, painting,
printing or spraying the desired area with a hydrophilic resin to encourage drainage
through wetting, or a hydrophobic material to discourage drainage.
[0097] The structure of the watermark formation elements 20 may also be designed to allow
sideways (lateral) drainage of liquid below the watermark forming surface 21, one
example of which is shown in Figures 7a to 7d. The first layer 30, which forms a substantial
portion of the watermark forming surface 21, has a mesh like construction with square
front surface apertures 23. The underlying second layer 31 is provided with apertures
34 in the form of channels extending across from one edge of the layer 31 to an opposing
edge. The third layer 32, which in this embodiment forms the drainage surface 25,
is also provided with apertures 35 in the form of channels extending across from one
edge of the layer 31 to the other in a similar direction to those of the second layer
31. The channels of the third layer have a greater width to those of the second layer
31. This structure produces a watermark formation element 20 having a cross section
as shown in Figure 7a. Thus in addition to the drainage channels 22 which extend through
the watermark formation element 20 from the watermark formation surface 21 to the
drainage surface 25, one or more additional drainage channels are provided which extend
laterally within the watermark formation element 20 beneath the watermark forming
surface. These laterally extending drainage channels may extend from one side of the
watermark formation element 20 to another as shown in Figures 7a-7d. Alternatively
they may simply extend from one point on the perimeter of the watermark formation
element 20 to another point. These drainage channels may be straight, angled, curved
or any other suitable shape, and may extend in the machine or cross-direction. The
lateral drainage channels may lie in a single plane (or layer 30-33) or they may be
stepped across two or more layers 30-33.
[0098] Although the watermark formation element illustrated in Figures 7a-7d is described
as having single first, second and third layers 30,31,32 the same may apply where
each of the 30,31,32 is formed from a plurality of layers described previously. Additionally,
although the illustrated example shows three layers 30, 31, 32, the number of layers
forming the watermark formation element 20 is not restricted. Furthermore, different
layers from those shown may have the laterally extending apertures 35.
[0099] The watermark formation elements 20 described above can therefore combine the advantages
of contour formed watermarks (embossed cylinder mould watermarks) and restricted drainage
formed watermarks (electrotype watermarks) to obtain greater contrast between the
light and dark areas of a watermark and very light areas. They also relieve a number
of the design constraints arising from cylinder mould and electrotype watermarks,
in particular:-
- unlike with the usual electrotype method, the watermark formation elements 20 can
be used to form any part of the watermark;
- the watermark formation elements 20 are not limited to specific dimensions in order
to obtain good clarity and contrast compared to the background, as are traditional
electrotypes. The use of such watermark formation elements 20 allows for a greater
range be used more flexibly in order to achieve a greater range of artistic effects.
In particular the electrotype image contrast can be reduced by reducing the thickness
if such an effect is desirable from an aesthetic point of view. Such subtleties may
also contribute to enhanced security by increasing the complexity of the image tonality;
- where the finished document requires a combination of cylinder mould and electrotype
watermarks, the location of the electrotypes relative to the embossings has always
been constrained because of the manufacturing issues and problems described previously.
These no longer apply as a single watermark formation element 20 may be used to provide
equivalent watermarks. This does not apply to the watermark formation elements 20
of the present invention as it is possible to create deeper areas within the profile
of the watermark formation surface 21 and provide solid areas within the deeper areas,
as well as in the higher areas;
- in a traditional process which has electrotypes, there is a manufacturing, and therefore
design, constraints on the number of electrotypes per mould cover and their location.
This is because they are usually attached using a robotic arm, which is a time consuming
process.
[0100] The use of watermark formation elements 20, as opposed to embossing the wire cloth
10 of the cylinder mould cover or attaching electrotypes thereto, provides the ability
to produce complex multitonal designs or images can be created with sharply contrasting
dark and very light areas adjacent each other. However it brings a number of additional
manufacturing challenges.
[0101] Durability of the resulting cylinder mould cover is extremely important as it is
subjected to significant stresses. The stresses may result from a couch roll, dandy
roll or the felt (formex) depending on the configuration of the paper machine. In
a machine which uses a couch roll, for example, the couch roll rotates in contact
with the cylinder mould and is used to transfer the partially formed paper web from
the cylinder mould cover to the felt (formex) which carries the web from the wet end
of the papermaking machine to the press section. There is therefore a significant
pressure formed between the cylinder mould and the couch roll. This means that, where
there is any element protruding from the surface of the wire cloth 10, there will
be a constantly repeating additional stress to the wire cloth 10.
[0102] The watermark formation elements 20 may also be provided with shock absorbing properties,
which enable the watermark formation element 20, and therefore the cylinder mould
cover, to withstand the pressure from the couch roll. This may be achieved by making
the whole, or a part, of the watermark formation element 20 from a resilient material,
such as rubber.
[0103] Alternatively, the watermark formation element 20 may comprise a support layer 40,
as an additional layer to those described previously, at the back of the watermark
formation element 20 either behind or forming the drainage surface 25. For example,
referring to the previously described embodiments, the support layer 40 may be located
on the back of the fourth layer(s) 33 in Figures 6a-6e or the third layer 32 in Figures
7a-7d.
[0104] Alternatively the support layer 40 may be one or more of the layers 30,31,32,33 of
these previously described embodiments.
[0105] The support layer 40 may be made from a resilient material. In the embodiment shown
in Figure 8, the support layer 40 is an additional layer located at the back of the
watermark formation element 20. The support layer 40 may be attached to the watermark
formation element 20 by any suitable means, for example UV cured resin.
[0106] The support layer 40 may be made from a material which has a different tensile modulus
from the main body of the watermark formation element 20. Preferred minimum and maximum
values for the tensile modulus of a conventional material used for the main body of
the watermark formation element 20 and for a shock absorbing, rubber like polymer
material, for the support layer 40 are given below with the more preferred values
shown in brackets.
|
Conventional material |
Shock absorbing (rubber like) polymer |
Property |
Min |
Max |
Min |
Max |
Tensile Modulus (Mpa) |
110 (500) |
12000 (5000) |
0.5 (2) |
100 (50) |
The following standard test methods may be used for measuring tensile modulus:-
- ASTM D638 - This is for non elastomeric materials and therefore would apply to the
conventional materials in the above table;
- ASTM D412 - This is for elastomers such as a rubber like materials and applies to
the shock absorbing materials in the table.
[0107] Alternatively the support layer 40 may have a structure which is resilient. In the
embodiment shown in Figure 9, the support layer 40 is located at the back of the watermark
formation element 20. The support layer 40 is formed from a series of springs (which
may be leaf, volute, coil, zigzag or other types of spring configurations).
[0108] Alternatively the support layer 40 may have a honeycomb or tessellated structure.
[0109] It is important that the support layer 40 has a shape and/or configuration which
does not interfere with the drainage flow through the drainage surface 25 of the watermark
formation element 20 or the backing layer(s) of the wire cloth 10. In any of these
embodiments, the support layer 40 must therefore have apertures which ensure that
the support layer 40 does not interfere with the drainage requirements identified
above and/or which form part of the drainage channels 22.
[0110] In a further alternative construction (see Figure 10), the watermark formation element
20 comprises an annular resilient support layer 40 which extends around the circumference
of the watermark formation element 20.
[0111] The method used to locate and/or attach one or more of the aforementioned watermark
formation elements 20 to the wire cloth 10 is also an important factor in ensuring
the durability of the cylinder mould cover. The following description refers to the
location/attachment of a single watermark formation element 20 to the wire cloth 10.
In the embodiment illustrated in Figures 8, 9 and 11, the wire cloth 10 is formed
from a face cloth 11, first backing layer 12, a second backing layer 14 and, in the
case of Figure 10 only, a third backing layer 16. The face cloth 11 and first backing
layer 12 each have a cut out area 15a, 15b respectively. The cut out area 15a in the
face cloth 11 is smaller than that in the first backing layer 12 and is substantially
the same size as, or slightly larger than, an upper section 41 of the watermark formation
element 20. This allows the upper section 41 to pass through the cut out area 15a.
The support layer 40 of the watermark formation element 20 and/or a lower section
42 of the watermark formation element 20 has at least one cross sectional dimension
which is greater than that of the cut out area 15a in the face cloth 11, but is the
same or slightly smaller than the cut out area 15b in the first backing layer 12.
This enables the watermark formation element 20 to be anchored between the layers
of the wire cloth 10. The rear surface of the watermark formation element 20 (whether
this is the drainage surface 25 or the support layer 40) is located against, and supported
by, the second backing layer 14.
[0112] Alternatively a watermark formation element 20 may be at least partly located in
a recess 43 in the face cloth 11 of the cylinder mould cover as shown in Figure 12.
The recess 43 is preferably formed by embossing the face cloth 11 (and possibly also
the underlying first backing layer 12). The recess 43 is preferably shallow (for example
between 0.5mm and 2mm deep). The recess 43 is preferably arranged so that the watermark
formation element 20 is pushed up against a locating corner. The watermark formation
element 20 is thus protected by the surrounding walls of the recess 43.
[0113] Figure 13 shows an alternative arrangement in which the face cloth 11 is provided
with a cut out area 15 (similar to the cut out area 15 illustrated in Figures 8 and
9) through which a watermark formation element 20 projects. The first backing layer
12 is provided with a recess 43 in which a watermark formation element 20 may be at
least partly located.
[0114] These are not the only suitable constructions. In other variations, some or all of
the layers of the wire cloth 10 may be provided with cut out areas 15 and/or recesses
43.
[0115] One or more watermark formation elements 20 may also be attached to one or more layers
of the wire cloth 10. Suitable methods of attaching a metallic watermark formation
element 20 to the wire cloth 10 are resistance or laser welding and soldering. Plastic
welding may be used to attach polymeric watermark formation elements 20. Alternatively,
the watermark formation element(s) 20 may be sewn, for example with a fine wire, onto
the wire cloth 10. The watermark formation element(s) 20 may also be adhered to the
wire cloth 10, for example with a UV cured resin or another suitable adhesive.
[0116] One or more fixings 45 may be used to attach one or more watermark formation elements
20 to one or more layers of the wire cloth 10. Such fixings 45 may be threaded metal
inserts, weldable metal inserts, flanged plastic or metal components, staples, components
with bendable legs and so on. The fixings 45 are preferably porous or hollow (e.g.
tubular).
[0117] Figure 14 illustrates one type of suitable fixing 45. This comprises a shank 46,
which may be a wire or plastic filament or an elastic thread, which passes through
one or more layers of the wire cloth 10 and a drainage channel 22 of the watermark
formation element 20. One end of the shank 46 has foot 47 integrally formed thereon
or attached thereto. The foot 47 may at least one dimension greater than that of the
wire mesh opening in the rearmost backing layer to which the fixing 45 is attached,
in the illustrated example first backing layer 12. The opposite end of the shank 46
is threaded through the drainage channel 22 and a head 48 is attached thereto or formed
thereon. The size of the head 48 is greater than the size of the front surface aperture
23 of the drainage channel 22 to ensure that the watermark formation element 20 is
held securely in position. One or more fixings 45 may be used per watermark formation
element 20.
[0118] Figure 15 illustrates the use of another form of suitable fixing 45. This has a flexible
shank 46, which may be a wire or plastic filament or an elastic thread. The shank
46 passes through one or more layers 11,12,14,16 of the wire cloth 10, up one drainage
channel 22, across the watermark formation surface 21, down an adjacent drainage channel
22. And back through the one or more layers 11,12,14,16 of the wire cloth 10. Feet
47 are formed on, or attached to, each end of the shank 46, which feet 47 have at
least one dimension greater than that of the wire mesh opening in the rearmost backing
layer to which the fixing 45 is attached.
[0119] Figure 16 illustrates the use of yet another suitable form of fixing 45. This comprises
a tubular or porous barbed spigot which extends from the drainage surface 25 of the
watermark formation element 20 through one or more layers of the wire cloth 10. In
the illustrated embodiment, the watermark formation element 20 is located in cut out
areas 15a, 15b in the face cloth 11 and first backing layer 12, so the spigot is pushed
through the wire mesh openings in the second and third backing layers 14,16. The spigot
has a central drainage passage 50 and its distal end is provided with one or more
barbs 49 which hook on the wire of the rearmost backing layer through which the spigot
passes; in the illustrated embodiment this is the third backing layer 16.
[0120] Figure 17 illustrates the use of yet another suitable fixing 45. This is in the form
of a wire which extends from the drainage surface 25 of the watermark formation element
20 through one or more layers of the wire cloth 10. In the illustrated embodiment
the watermark formation element 20 is located in cut out areas 15a, 15b in the face
cloth 11 and first backing layer 12, and the wire is threaded through a wire mesh
opening in the second backing layer 14. The end of the wire is bent over to form a
hook 51.
[0121] The aforementioned fixings 45 may additionally be adhered or welded to the wire cloth
10 to ensure that they are firmly attached.
[0122] To enable the attachment of the watermark formation element 20 to the wire cloth
10 by means of fixings, one or more of the layers forming the wire cloth 10 may need
to be provided with additional or larger holes for receiving the fixings 45.
[0123] The aforementioned watermark formation elements 20 can be produced by 3D printing
or another suitable manufacturing process, such as injection moulding, laser ablation,
vacuum formation, machining etc.
[0124] 3D printing, also known as rapid prototyping or additive manufacturing, is a relatively
new technology, which uses a digital model, usually created by some form of computer
aided design (CAD) package or a 3D scanner, to create a 3 dimensional object. The
3D printer reads the data from the CAD drawing and lays down successive layers of
material to build up a physical object from a series of cross sections. There are
a large number of different 3D printing processes, including (but not limited to)
stereolithography (SLA), Selective Laser Sintering (SLS), Selective Laser Melting
(SLM), Laminated Object Manufacturing (LOM), Fused Deposition Modelling (FDM), Solid
Ground Curing (SGC), Direct Metal Laser Sintering (DMLS), electron beam melting (EBM)
and ink jet printing techniques.
[0125] 3D printing methods may be used to manufacture the watermark formation elements 20
from a variety of materials. Examples include one or more polymeric materials, one
or more metals or a combination of both metals and polymers, for example with a metal
incorporated into a polymer matrix. The material or materials selected for the watermark
formation elements 20 need to be sufficiently durable to with stand the pressure created
between the cylinder mould and the couch roll and the continuous percussion therefrom.
The selection of the material(s) will also depend on the 3D printing process used.
[0126] Some examples of suitable polymeric materials are given below, although this list
is not exhaustive:-
For fused deposition manufacture (FDM):
- acrylonitrile butadiene styrene (ABS)
- polyphenylsulphone (PPS, PPSU or PPSF)
- polylactic acid (PLA)
- polyamide (PA)
- polycarbonate (PC)
- blends of materials, for example PC-ABS
For selective laser sintering (SLS):
- Nylon, notably PA12
- glass filled PA12
For inkjet or 'photojet' type processes (UV curing resins):
- acrylic
- simulated ABS
- simulated polypropylene(PP)
- rubber like grades
- dental grades
- biocompatible grades
[0127] Some examples of suitable metals are given below, although this list is not exhaustive:-
For selective laser sintering (SLS) or selective laser melting (SLM) of metal powders:
- titanium, pure and alloys
- Steels, including stainless steels
- nickel-chromium alloys
- aluminium, pure and alloys
- cobalt-chromium alloys
- copper and copper alloys
[0128] Advantageously watermark formation elements 20 comprising more than one different
material can be formed using a single device, such as a 3D printer, as some commercial
3D printers e.g. Stratasys' Objet 350 Connex model, are able to print multiple materials.
This enables both multi-coloured products and composite structures, e.g. combined
rigid and rubberlike polymers, to be produced in a single process.
[0129] A significant advantage of using a 3D printing process to form the watermark formation
element(s) 20 is that the time taken to manufacture a cylinder mould cover, and therefore
the cost, is significantly reduced compared to the traditional process, as the artwork
is used directly to form the watermark formation elements 20. There is no longer a
need to produce embossing dies, which must then be used to emboss the cylinder mould
cover. The use of a computer controlled process for forming each individual watermark
formation element 20 makes it possible to customise each individual watermark, for
example for unique passport pages or banknote serial numbers.
[0130] A further advantage of 3D printing is that it makes it considerably easier to accommodate
shrinkage. As the paper web passes through the various stages of the papermaking process,
it shrinks. The degree of shrinkage at the edge of the paper web is greater than in
the centre and may vary according to the particular machine, wetness, type of stock
processing speed used. To get a uniform finished document width, the actual document
width on the cylinder mould cover during manufacture has to vary to compensate for
shrinkage. The design of any watermark must also allow for shrinkage. Using 3D printing
means that the watermark formation elements 20 can easily be adjusted, depending on
where on the width of the cylinder mould cover they are located.
[0131] Another advantage of 3D printing is that many of the methods described above can
be used to form the watermark formation elements 20 directly on the wire cloth 10
of the cylinder mould cover with no need for additional fixings 45.
[0132] Alternatively one or more watermark formation elements 20 may be formed onto a section
of wire mesh which is subsequently attached to the wire cloth 10, for example to the
face cloth 11, of the cylinder mould cover with suitable fixings 45.
[0133] 3D pens are also available, such as 3Doodler (TM) or Lixpen (TM). These can be used
to attach the watermark formation elements 20 to the wire cloth 10 by drawing loops
from a 3D printed watermark formation element 20 around the wires of the face cloth
11 and back to the watermark formation element 20. Such 3D pens may also be used with
the watermark formation elements 20 which have been manufactured by a method other
than 3D printing.
[0134] As another alternative, the watermark formation elements 20 may be attached to a
perforated skin or sleeve, which fits over a traditional wire cloth 10.
[0135] Another advantage of 3D printing is that it provides flexibility. For example the
resulting mould cover may have attached thereto a number of discrete watermark formation
elements 20 at regular intervals, each watermark formation element 20 being designed
to produce a single watermark. The watermark formation elements 20 may all be designed
to produce the same watermark, or different watermarks.
[0136] As described previously a number of webs may be produced simultaneously on a cylinder
mould papermaking machine. The webs are cut to form a number of smaller interim sheets,
and the interim sheets are cut to form a number of smaller documents (usually after
printing). Each watermark formation element 20 may be the same size as a single document
(see Figure 18) and be designed to produce all the watermarks (and holes or apertures)
required for a single document. This may include several different watermarks 52a,
52b, 52c, 52d. These watermarks 52a, 52b, 52c, 52d may be, inter alia, pictorial watermarks,
corner reinforcing watermarks, security thread tracks and/or electrotype style alphanumeric
watermarks. Sufficient identical watermark formation elements 20 may be attached to
the wire cloth 10 adjacent each other (to form a tessellated sheet section as shown
in Figure 19) to produce an interim sheet which, when slit, will form a number of
identical smaller documents all having the same combination of watermarks 52a, 52b,
52c, 52d. This may be repeated around the circumference of the mould cover, so that
at least one of the paper webs can be split to form identical interim sheets and then
identical documents.
[0137] The use of the aforementioned watermark formation elements 20 in the manufacture
of paper is particularly advantageous where each one designed to produce multiple
watermarks 52a, 52b, 52c, 52d. During the papermaking process, the paper shrinks at
an uneven rate across the web. Thus, in order to ensure that the watermarks 52a, 52b,
52c, 52d in the finished document are correctly positioned, the position of the elements
of the watermark formation surface 21 which produce the individual watermarks 52a,
52b, 52c, 52d may vary depending on where on the web the watermark is being formed.
The use of 3D printing simplifies this process.
[0138] Figure 21 provides a clear illustration of a section of a watermark formation surface
21 of a watermark formation element 20, part of which has a contoured profile. In
this example, one watermark (in the shape of a bird of which a section of the bird's
wing is shown) has raised and sunken elements. This produces a watermark similar to
that of a prior art cylinder mould watermark. Another watermark is formed from solid
areas 21 in the form of the numerals "0", which are raised above the rest of the watermark
formation surface 21. This produces a watermark similar to that of a prior art electrotype
watermark.
[0139] It is also possible to use different sets of watermark formation elements 20 to form
different sheets or webs, which means that more than one type of document may be produced
simultaneously on a single cylinder mould.
[0140] Alternatively, instead of tessellating a number of individual identical watermark
formation elements 20 to enable an interim sheet to be produced, a single watermark
formation element 20 can made, which is designed to produce all the required watermarks
52a, 52b, 52c, 52d for multiple documents (see Figure 20). In addition the watermark
formation element 20 can be used to provide slitter/chop guide marks 52e, which are
used to assist in the accurate cutting of the webs/sheets. Margins may also be included
between the areas which will form an individual document, which can be used as fixing
points. Fixing points are required for attaching different sets of watermark formation
elements 20 used to form different webs either together or to the cylinder mould cover.
These will be cut away when the paper is slit into the individual interim sheets and
then the documents.
[0141] As a further alternative, the entire face cloth 11 of a cylinder mould cover may
be a watermark formation element 20 formed by 3D printing. In addition the backing
layers 12,14 may also be 3D printed.
[0142] Where the watermark formation element(s) 20 replaces the wire cloth 10 (cylinder
mould cover) it is formed into a sleeve which fits over the cylinder mould itself.
The sleeve may comprise a single sheet or a plurality of smaller sheets joined together.
Some suitable methods of joining sheets together are as follows:-
Figure 29 - a hinge joint may be used to join end to end of individual sheets to allow
forward and backward motion of the sheets.
Figure 30 - a spigot joint may be used to join the main body of the watermark formation
element 20 to the face cloth 11. The drainage surface 25 may have spigots that slot
into the wire of the face cloth 11.
Figure 31 - a clip lock joint may be used to join two ends of adjacent sheets by slotting
them end to end, enabling tight locking of the sheets at the joint.
Figure 32 - a socket joint may be used, which is similar to a ball and socket joint,
where a square end of a sheet is slotted and into square groove and locked into place.
Figure 33 - a lap joint may be used in which two sheets are joined end to end. The
fixing of the joint is completed by adding a clip to fix the two sheets together to
prevent one sheet from popping out.
[0143] In a traditional process using an embossed cylinder mould, the presence of many embossings
can make it difficult to hold the mould cover firm whilst the wire cloth 10 is being
embossed. The use of watermark formation elements 20 overcomes this disadvantage as
they are formed separately.
[0144] Advantageously, the watermark formation elements 20 are produced so as not to have
the knuckles associated with the woven wire mesh of the face cloth. This eliminates
interference of the watermark image by the image of the wire knuckles which is inevitably
produced in the paper.
[0145] Further manufacturing problems may arise where a watermark is to be combined with
another security feature, such as traditionally formed corner reinforcing watermarks
as described in
EP-A-1468142 or security threads. In these cases the order or steps in manufacturing the wire
cloth is important. For example any embossings required for these other security features
may need to be carried out before any cut out areas 15 are formed (for example by
laser cutting) to prevent distortion of the wire mesh from occurring which may affect
watermark formation elements 20. The watermark formation elements 20 may then be inserted
into the recesses 43 or through the cut out areas 15 as required.
[0146] The watermarked paper thus produced is suitable for many applications, including
paper used in banknotes, passports, certificates, tickets and many more applications.
It is especially convenient for producing paper for passports, which have a complex
layout and require different watermarks on each page.
[0147] The present disclosure also provides embodiments as set out in the following clauses:-
- 1. A watermark formation element for forming at least one watermark in a paper, said
watermark formation element having an integrated body comprising a watermark forming
surface, which has one or more watermark forming regions, and a drainage surface,
said watermark formation element having a plurality of drainage channels extending
from front surface apertures in the watermark forming surface to the drainage surface,
said watermark formation element which has shock absorbing properties.
- 2. A watermark formation element of clause 1 in which the watermark formation element
is made from a resilient material which provides the shock absorbing properties.
- 3. A watermark formation element of clause 1 or clause 2 and in which the watermark
formation element comprises a support layer which has shock absorbing properties.
- 4. A watermark formation element of clause 3 in which the support layer is made from
a resilient material.
- 5. A watermark formation element of clause 3 in which the support layer has a resilient
structure.
- 6. A watermark formation element of clause 5 in which the support layer comprises
a plurality of springs or has a honeycomb or tessellated structure.
- 7. A watermark formation element of clauses 3 to 6 in which the support layer is an
annular layer which extends around the circumference of the watermark formation element.
- 8. A watermark formation element of clauses 3 to 6 in which the support layer is an
additional layer formed on the drainage surface.
- 9. A method of making a watermark formation element for a cylinder mould cover for
forming a plurality of watermarks in at least one web of paper, wherein the watermark
formation element is formed by a 3D printing process, and is configured to produce
at least one watermarked region and at least one non-watermarked region for a single
document cut from said at least one web.
- 10. A method of making a watermark formation element of clause 9 in which the watermark
formation element is configured to produce at least two watermarked regions for a
single document cut from said at least one web.
- 11. A method of making a watermark formation element of clauses 1 or 2 in which the
watermark formation element is configured to produce all required watermarked and
non-watermarked regions for a single document cut from said at least one web.
- 12. A method of making a watermark formation element for a cylinder mould cover for
forming a plurality of watermarks in at least one web of paper, wherein the watermark
formation element is formed by a 3D printing process, and is configured to produce
watermarked and non-watermarked regions for a plurality of identical documents cut
from said at least one web.
- 13. A method of making a watermark formation element for a cylinder mould cover for
forming a plurality of watermarks in at least one web of paper, wherein the watermark
formation element is formed by a 3D printing process, and is configured to produce
watermarked and non-watermarked regions for a plurality of non-identical documents
cut from said at least one web.
- 14. A method of making a watermark formation element for a cylinder mould cover for
forming a plurality of watermarks in at least one web of paper, wherein the watermark
formation element is formed by a 3D printing process, and is configured to produce
watermarked and non-watermarked regions for all documents cut from all webs formed
on the cylinder mould cover.
- 15. A method of making a cylinder mould cover comprising the step of making the or
each watermark formation element of any one of clauses 12 to 14 and subsequently attaching
the or each watermark formation element to a foraminous layer.
- 16. A method of making a cylinder mould cover comprising the step of making the or
each watermark formation element of any one of clauses 12 to 15 by forming the or
each watermark formation element directly on a foraminous layer.
- 17. A method of making a cylinder mould cover of clauses 15 or 16 wherein a first
watermark formation element is configured to form a plurality of watermarks in a first
plurality of identical documents produced from the paper and one or more further watermark
formation elements are configured to form one or more further pluralities of watermarks
in one or more further pluralities of identical documents produced from the paper.
- 18. A watermark formation element made by the method of clause 9 configured to produce
at least one watermarked region and at least one non-watermarked region for a single
document cut from said at least one web.
- 19. A watermark formation element made by the method of clause 10 or 11 configured
to produce all required watermarked and non-watermarked regions for a single document
cut from said at least one web.
- 20. A watermark formation element made by the method of clause 12 configured to produce
watermarked and non-watermarked regions for a plurality of identical documents cut
from said at least one web.
- 21. A watermark formation element made by the method of clause 13 configured to produce
watermarked and non-watermarked regions for a plurality of non-identical documents
cut from said at least one web.
- 22. A watermark formation element made by the method of clause 14 is configured to
produce watermarked and non-watermarked regions for all documents cut from all webs
formed on the cylinder mould cover.
- 23. A method of making watermarked paper comprising the step of depositing fibres
on a cylinder mould cover made by the method of any one of clauses 15 to 17.
- 24. Paper formed by the method of clause 23.
- 25. A secure document made from the paper of clause 24 comprising a banknote, a passport,
a certificate, a ticket or the like.
- 26. A watermark formation element for forming at least one watermark in a paper, said
watermark formation element having an integrated body comprising a watermark forming
surface, which has one or more watermark forming regions, and a drainage surface,
said watermark formation element having a plurality of drainage channels extending
from front surface apertures in the watermark forming surface to the drainage surface,
wherein the watermark forming surface comprises a plurality of first solid areas between
the drainage surface apertures and at least one second solid area between the drainage
surface apertures in the watermark forming regions, the at least one second solid
area having a larger cross sectional area than the first solid areas, and the cross
sectional area of the second solid area being at least three times that of each of
the drainage surface apertures.
- 27. A watermark formation element of clause 26 in which a surface of at least one
of the solid areas is planar.
- 28. A watermark formation element of clause 26 in which a surface of at least one
of the solid areas is rounded.
- 29. A watermark formation element of clause 26 in which the at least one second solid
area has a stepped profile.
- 30. A watermark formation element of any of clauses 26 to 29 in which the at least
one second solid area extends from the watermark formation surface to the drainage
surface.
- 31. A watermark formation element of any of clauses 26 to 30 in which the second solid
area covers a plurality of drainage channels, thereby closing them off.
- 32. A watermark formation element of any of clauses 26 to 31 in which the maximum
dimension of the solid areas is 2mm.