Patent Grant
10632780
1. Field of the Disclosure
The present disclosure 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.
2. Description of the Related Art
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.
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.
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.
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.
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.
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.
It is also very difficult to produce light watermark regions exhibiting a significant surface area using the embossed cylinder mould technique.
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 U.S. Pat. Nos. 1,901,049 and 2,009,185.
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 1.2 mm and the thickness is between 500 and 700 μm, to avoid such problems.
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.
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.
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.
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.
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.
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 (3×6) 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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
The disclosure 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, wherein at least some of the front surface apertures are shaped to define at least one of an alphanumeric, a symbol or a pictorial image, and further comprising a filter layer located between the watermark forming surface and the drainage surface having filter layer apertures which have a maximum width which is less than a smallest width of the front surface apertures which define the at least one of an alphanumeric, a symbol or a pictorial image.
Preferably the shape of the watermark formation element is an alphanumeric, symbol or pictorial image.
The disclosure also 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, wherein the front surface apertures are shaped to define at least two different shapes.
The disclosure also 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, wherein the shape of the watermark formation element is an alphanumeric, symbol or pictorial image.
Preferably at least some of the front surface apertures are shaped to define at least one of an alphanumeric, a symbol or a pictorial image.
The shape defined by the at least some of the front surface apertures is preferably the same as, or related in context to, the shape of the watermark formation element.
Preferably the at least one alphanumeric, symbol or pictorial image defined by the at least some of the front surface apertures is negative or is positive.
In a preferred embodiment at least one alphanumeric, symbol or pictorial image defined by the at least some of the front surface apertures is positive and at least one alphanumeric, symbol or pictorial image defined by the at least some of the front surface apertures is negative.
Preferably said watermark formation element is 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.
Preferably each layer is formed from a plurality of sub layers.
The layers and/or sub layers are preferably fused together to form the integrated body.
Preferably the watermark formation element is formed by 3D printing.
The watermark formation element may be formed from a polymeric material or a plurality of different polymer materials or from a metallic material or a plurality of different metallic materials.
Preferably the minimum cross-sectional area of the front surface aperture and of any section of the drainage channels is 0.01 mm2.
The shape of the drainage apertures in different layers may be different.
Preferably any one layer may have drainage apertures, the cross sectional area and/or shape of are not all the same.
The total cross sectional area of the front surface apertures preferably 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%.
The layers may be planar or non-planar.
Preferably the watermark formation surface is contoured in the one or more watermark forming regions to provide tonal variation in the paper formed thereon.
In a preferred embodiment the shape, size, spacing and or distribution of the drainage surface apertures is varied within the one or more watermark forming regions to provide tonal variation in the paper formed thereon.
Preferably the minimum width of the front surface apertures which are used to form the at least one alphanumeric, pictorial image or symbol lie in the range 0.1 to 5.0 mm, more preferably in the range of 0.3 to 3.0 mm, and most preferably in the range of 0.3 to 1.0 mm.
The width of the filter layer apertures 37 is preferably in the range of 0.1 to 1 mm and more preferably in the range of 0.4 to 1.0 mm.
The maximum distance from the watermark formation surface to the filter layer may be in the range of 0.1 to 3.0 mm, and preferably in the range of 0.3 to 2.00 mm.
The thickness of the filter layer may be in the range of 0.1 to 1.0 mm and preferably in the range of 0.3 to 0.6 mm.
The thickness of a layer which provides the drainage surface is preferably in the range of 0.6 to 6.0 mm and preferably in the range of 1 to 3.0 mm.
The invention further provides a cylinder mould cover for manufacturing a paper having at least one watermark, comprising a at least one foraminous layer and at least one watermark formation element attached thereto.
Preferably, the watermark formation element is located in a recess formed in the at least one foraminous layer or in a cut out portion formed in the least one foraminous layer.
Alternatively, the watermark formation element is located in a recess formed in the at least one foraminous layers and a cut out portion formed in another foraminous layer.
The disclosure 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.
The one or more watermark formation elements may be formed and subsequently attached to the least one foraminous layer.
Alternatively, the one or more watermark formation elements may be formed directly on the least one foraminous layer.
The disclosure further provides a method of making watermarked paper comprising the step of depositing fibres on the cylinder mould cover.
The disclosure further provides paper formed by this method.
The disclosure further provides a secure document made from this paper comprising a banknote, a passport, a certificate, a ticket or the like.
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:—
a and 28b are parts of different watermark formation surfaces of different watermark formation elements;
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.
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.
A typical prior art cylinder mould cover is formed from a multi-layered wire cloth 10, as shown in
To form electrotype watermarks, electrotypes 17 may be attached to the face cloth 11 by a suitable method, such as welding or soldering.
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.
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 (see
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
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
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.
From
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 2 mm; 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.
The solid areas 27 may be rounded (as shown in
The solid areas 27 of the watermark formation element 20 may form a regular pattern, for example the mesh like pattern as shown in
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.
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.
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
Where the front surface apertures 24 are at least one alphanumeric, a pictorial image or a symbol, the minimum width of the front surface apertures 24 is preferably in the range of 0.1 to 5.0 mm, more preferably in the range of 0.3 to 3.0 mm and most preferably in the range of 0.3 to 1.0 mm. In particular, if the front surface apertures define alphanumerics, the stem width of any character (where it acts a front surface aperture 24) is preferably no thinner than 0.3 mm in width and the space between the characters (the solid areas 27 between the front surface apertures 24) is preferably no smaller than 0.3 mm. 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 0.3 mm 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.
Where the front surface apertures 24 are used to define one or more alphanumerics, a pictorial image or a symbol, in order to make the resulting image(s) clearly defined, the total open cross sectional area of the front surface apertures 24 may be such that paper fibres can penetrate and block the drainage channels 22. This may prevent further drainage and prevent the appropriate amount of fibre build up, leading to poorly formed images. In some instances the paper fibres may pass through the drainage channels 22 altogether, which could lead to holes in the paper. In order to prevent this from occurring, at least one filter layer 36 is located between the watermark forming surface 21 and the drainage surface 25. The filter layer 36 has filter layer apertures 37 which are sized to prevent the paper fibres from passing to far into, or through, the drainage channels 22 to prevent this problem from occurring.
Where the watermark formation element 20 is made up from multiple layers, the filter layer 36 may form one of the middle layers (e.g. replacing the second layer 31 or third layer 32 of
The width of the front surface apertures 23 which are used to form the alphanumeric, pictorial image or symbol preferably lie in the range of 0.1 to 5.0 mm, more preferably in the range of 0.3 to 3.0 mm, and most prefereably in the range of 0.3 to 1.0 mm. The width of the filter layer apertures 37 is preferably in the range of 0.1 to 1 mm and more preferably in the range of 0.4 to 1.0 mm. The size selected, however, will depend on the widths of the front surfaces apertures 23 which are used to form the alphanumeric, pictorial image or symbol. In any area of the watermark formation element 20 in which there are front surface apertures 23 which are not used to form the alphanumeric, pictorial image or symbol, the minimum width of the front surface apertures 23 may be the same or smaller than the minimum width of the filter layer apertures 37.
The effectiveness of the filter layer 36 can be affected by its distance from the watermark formation surface 21. Therefore, the preferred maximum distance, which equates to the maximum thickness of the first layer(s) (30), is in the range of 0.1 to 3.0 mm, and more preferably in the range of 0.3 to 2.00 mm. The thickness of the filter layer 36 is preferably in the range of 0.1 to 1.0 mm and more preferably in the range of 0.3 to 0.6 mm. The preferred thickness of the third layer 32 is preferably in the range of 0.6 to 6.0 mm and more preferably in the range of 1 to 3.0 mm.
As shown in
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.
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.
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
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.
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 to achieve this. Some examples of watermark formation elements 20 used to form a watermark in the form of a portrait are illustrated in
The drainage surface apertures 24 may positively define a shape (such as the circle in
In the example illustrated in
The spacing between the front surface apertures 24 can also be varied to provide tonal variation. 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
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
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.
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 20 gsm.
Thus for a 90 gsm paper the grammage may range from approximately 20 gsm to up to approximately 200 gsm.
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.
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.
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
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.
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.
In one example, as shown in
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.
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.
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.
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%.
The layers 30,31,32,33 illustrated in
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 0.1 mm. 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.
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.
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.
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
Although the watermark formation element illustrated in
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:—
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.
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.
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.
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
Alternatively the support layer 40 may be one or more of the layers 30,31,32,33 of these previously described embodiments.
The support layer 40 may be made from a resilient material. In the embodiment shown in
Alternatively the support layer 40 may have a structure which is resilient. In the embodiment shown in
Alternatively the support layer 40 may have a honeycomb or tessellated structure.
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.
In a further alternative construction (see
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
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
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.
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.
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).
The aforementioned fixings 45 may additionally be adhered or welded to the wire cloth 10 to ensure that they are firmly attached.
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.
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.
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.
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.
Some examples of suitable polymeric materials are given below, although this list is not exhaustive:—
For fused deposition manufacture (FDM):
For selective laser sintering (SLS):
For inkjet or ‘photojet’ type processes (UV curing resins):
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:
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.
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.
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.
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.
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.
3D pens are also available, such as 3Doodler™ or Lixpen™. 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.
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.
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.
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
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.
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.
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
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.
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.
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.
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.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1419983.0 | Nov 2014 | GB | national |
This application is a continuation of International Application No. PCT/GB2015/053391 filed on Nov. 9, 2015, which claims the benefit of British Application No. GB 1419983.0 filed Nov. 10, 2014, the entire contents of both of which are incorporated by reference herein.
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| Number | Date | Country | |
|---|---|---|---|
| 20170239973 A1 | Aug 2017 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/GB2015/053391 | Nov 2015 | US |
| Child | 15591940 | US |
