The invention relates to methods and apparatus for producing a printed product, for example for use in the manufacture of security documents and security devices.

Security devices are typically used on security documents such as banknotes, cheques, passports, identity cards, certificates of authenticity, fiscal stamps and other secure documents, in order to confirm their authenticity.

Articles of value, and particularly documents of value such as banknotes, cheques, passports, identification documents, certificates and licences, are frequently the target of counterfeiters and persons wishing to make fraudulent copies thereof and/or changes to any data contained therein. Typically such objects are provided with a number of visible security devices for checking the authenticity of the object. By "security device" we mean a feature which it is not possible to reproduce accurately by taking a visible light copy, e.g. through the use of standardly available photocopying or scanning equipment. Examples include features based on one or more patterns such as microtext, fine line patterns, latent images, Venetian blind devices, lenticular devices, moire interference devices and moire magnification devices, each of which generates a secure visual effect. Other known security devices include holograms, watermarks, embossings, perforations and the use of colour-shifting or luminescent / fluorescent inks. Common to all such devices is that the visual effect exhibited by the device is extremely difficult, or impossible, to copy using available reproduction techniques such as photocopying. Security devices exhibiting non-visible effects such as magnetic materials may also be employed.

One class of security devices are those which produce an optically variable effect, meaning that the appearance of the device is different at different angles of view. Such devices are particularly effective since direct copies (e.g. photocopies) will not produce the optically variable effect and hence can be readily distinguished from genuine devices. Optically variable effects can be generated based on various different mechanisms, including holograms and other diffractive devices, moire interference and other mechanisms relying on parallax such as Venetian blind devices, and also devices which make use of focussing elements such as lenses, including moire magnifier devices, integral imaging devices and so-called lenticular devices.

Some security devices may involve the provision of a focussing element array and an image array located approximately in the focal plane of the focussing element array such that the focussing element array exhibits a substantially focussed image of the image array. This focussed image may preferably be optically variable and could for example be based on any of the mechanisms detailed below.

Moire magnifier devices (examples of which are described in EP-A-1695121 , WO-A-94/27254, WO-A-2011/107782 and WO2011/107783) make use of an array of focusing elements (such as lenses or mirrors) and a corresponding array of microimages, wherein the pitches of the focusing elements and the array of microimages and/or their relative locations are mismatched with the array of focusing elements such that a magnified version of the microimages is generated due to the moire effect. Each microimage is a complete, miniature version of the image which is ultimately observed, and the array of focusing elements acts to select and magnify a small portion of each underlying microimage, which portions are combined by the human eye such that the whole, magnified image is visualised. This mechanism is sometimes referred to as "synthetic magnification". The magnified array appears to move relative to the device upon tilting and can be configured to appear above or below the surface of the device itself. The degree of magnification depends, inter alia, on the degree of pitch mismatch and/or angular mismatch between the focusing element array and the microimage array. Integral imaging devices are similar to moire magnifier devices in that an array of microimages is provided under a corresponding array of lenses, each microimage being a miniature version of the image to be displayed. However here there is no mismatch between the lenses and the microimages. Instead a visual effect is created by arranging for each microimage to be a view of the same object but from a different viewpoint. When the device is tilted, different ones of the images are magnified by the lenses such that the impression of a three-dimensional image is given. "Hybrid" devices also exist which combine features of moire magnification devices with those of integral imaging devices. In a "pure" moire magnification device, the microimages forming the array will generally be identical to one another. Likewise in a "pure" integral imaging device there will be no mismatch between the arrays, as described above. A "hybrid" moire magnification / integral imaging device utilises an array of microimages which differ slightly from one another, showing different views of an object, as in an integral imaging device. However, as in a moire magnification device there is a mismatch between the focusing element array and the microimage array, resulting in a synthetically magnified version of the microimage array, due to the moire effect, the magnified microimages having a three-dimensional appearance. Since the visual effect is a result of the moire effect, such hybrid devices are considered a subset of moire magnification devices for the purposes of the present disclosure. In general, therefore, the microimages provided in a moire magnification device should be substantially identical in the sense that they are either exactly the same as one another (pure moire magnifiers) or show the same object/scene but from different viewpoints (hybrid devices).

Moire magnifiers, integral imaging devices and hybrid devices can all be configured to operate in just one dimension (e.g. utilising cylindrical lenses) or in two dimensions (e.g. comprising a 2D array of spherical or aspherical lenses).

Lenticular devices on the other hand do not rely upon magnification, synthetic or otherwise. An array of focusing elements, typically cylindrical lenses, overlies a corresponding array of image sections, or "slices", each of which depicts only a portion of an image which is to be displayed. Image slices from two or more different images are interleaved and, when viewed through the focusing elements, at each viewing angle, only selected image slices will be directed towards the viewer. In this way, different composite images can be viewed at different angles. However it should be appreciated that no magnification typically takes place and the resulting image which is observed will be of substantially the same size as that to which the underlying image slices are formed. Some examples of lenticular devices are described in US-A-4892336, WO-A- 2011/051669, WO-A-201 1051670, WO-A-2012/027779 and US-B-6856462. More recently, two-dimensional lenticular devices have also been developed and examples of these are disclosed in WO-A-2015/01 1493and WO-A-2015/011494. Lenticular devices have the advantage that different images can be displayed at different viewing angles, giving rise to the possibility of animation and other striking visual effects which are not possible using the moire magnifier or integral imaging techniques.

Security devices such as moire magnifiers, integral imaging devices and lenticular devices, as well as others involving the use of focusing elements, depend for their success significantly on the resolution with which the image array (comprising e.g. microimages or image elements) can be formed. Since the security device must be thin in order to be incorporated into a document such as a banknote, any focusing elements required must also be thin, which by their nature also limits their lateral dimensions. For example, lenses used in such security elements preferably have a width or diameter of 50 microns or less, e.g. 30 microns. In a lenticular device this leads to the requirement that each image element must have a width which is at most half the lens width. For example, in a "two channel" lenticular switch device which displays only two images (one across a first range of viewing angles and the other across the remaining viewing angles), where the lenses are of 30 micron width, each image element must have a width of 15 microns or less. More complicated lenticular effects such as animation, motion or 3D effects usually require more than two interlaced images and hence each element needs to be even finer in order to fit all of the image elements into the optical footprint of each lens. For instance, in a "six channel" device with six interlaced images, where the lenses are of 30 micron width, each image element must have a width of 5 microns or less.

Similarly high-resolution image elements are also required in moire magnifiers and integral imaging devices since approximately one microimage must be provided for each focusing element and again this means in effect that each microimage must be formed within a small area of e.g. 30 by 30 microns. In order for the microimage to carry any detail, fine linewidths of 5 microns or less are therefore highly desirable. Conventional processes used to manufacture image elements for security devices are based on printing and include intaglio, gravure, wet lithographic printing as well as dry lithographic printing. The achievable resolution is limited by several factors, including the viscosity, wettability and chemistry of the ink, as well as the surface energy, unevenness and wicking ability of the substrate, all of which lead to ink spreading. With careful design and implementation, such techniques can be used to print pattern elements with a line width of between 25 pm and 50 pm. For example, with gravure or wet lithographic printing it is possible to achieve line widths down to about 15 pm. However, even these small dimensions are not sufficient in many cases to achieve the desired effects and indeed achieving these dimensions in a metal surface using conventional de-metallisation techniques is very difficult.

In accordance with a first aspect of the present invention, a method of producing a printed product comprises:

(a) providing a plurality of recesses in a first surface of a transfer member, the transfer member having opposed first and second surfaces;

(b) providing a first curable material in said recesses;

(c) curing the first curable material in said recesses;

(d) applying a pattern support layer of a second curable material on to the first surface of the transfer member, the pattern support layer being provided over the recesses;

(e) exposing the second surface of the transfer member to curing radiation, the transfer member being formed of a material that allows said curing radiation to travel therethrough whereby the cured material in the recesses acts to prevent curing radiation reaching the pattern support layer overlying the recesses while radiation reaching the second curable material offset from the recesses is cured; (f) bringing the transfer member into contact with a first substrate;

(g) curing uncured parts of the pattern support layer while it contacts the first substrate; and

(h) separating the first substrate from the transfer member whereby the cured first curable material and the associated, cured pattern support layer transfers onto the substrate.

In accordance with a second aspect of the present invention, apparatus for producing a printed product comprises:

a) a transfer member having opposed first and second surfaces, a plurality of recesses being provided in the first surface of the transfer member;

b) apparatus for providing a first curable material in said recesses;

c) apparatus for curing the first curable material in said recesses;

d) apparatus for applying a pattern support layer of second curable material onto the first surface of the transfer member, the pattern support layer being provided over the recesses;

e) apparatus for exposing the second surface of the transfer member to curing radiation, the transfer member being formed of a material that allows said curing radiation to travel therethrough whereby the cured material in the recesses acts to prevent curing radiation reaching the pattern support layer overlying the recesses while radiation reaching the second curable material offset from the recesses is cured; and f) apparatus for curing uncured parts of the pattern support layer while it contacts a first substrate.

We have developed a new method and apparatus which has particular application in the context of a metalized first substrate and which can generate an image mask (the transferred cured first curable material and associated, cured pattern support layer) which can then be used in a subsequent de- metallisation process. The method enables very high resolution images to be produced with typical dimensions less than 10 pm even down to 2 pm or less. This is achieved by utilising the cured, first curable material in the recesses as a mask to achieve selective curing of the pattern support layer whereby the uncured portions of the pattern support layer are precisely registered with the recesses and are then used to transfer the first cured material from the recesses onto the first substrate. As explained above, the invention is particularly concerned with producing printed products for use in security devices that produce an optically variable effect and in these cases, the recesses typically define images, preferably microimages. Thus, in preferred embodiments, the recesses define an array of images or image portions suitable for use in a micro-optic device such as a lenticular device, moire magnifier, or integral imager.

The first curable material in the recesses could be cured in a variety of conventional ways by heating or the like and in the preferred embodiments step c) comprises irradiating the first curable material in the recesses with curing radiation. Typical examples of curing radiation include UV, IR, and thermal radiation. The form of radiation will be chosen that corresponds to an absorber provided in the first curable material.

In some cases, in step (b), the first curable material will only partially fill the recesses. This would then allow a further curable material to be added, for example to generate specific colours if one or both of the curable materials is partially transparent and they have different colours and are visible, or would mean that some of the pattern support layer would be received in the recesses. However, in the preferred embodiments, the first curable material substantially fills the recesses.

Any suitable curable material could be used for the first curable material such as a thermally-curable resin or lacquer, for example an intaglio ink. Typically, the ink will include at least one dye. However, preferably, the first curable material is a radiation curable material, preferably a UV curable material. UV curable polymers employing free radical or cationic UV polymerisation are suitable for use as the UV curable material. Examples of free radical systems include photo- crosslinkable acrylate-methacrylate or aromatic vinyl oligomeric resins. Examples of cationic systems include cycloaliphatic epoxides. Hybrid polymer systems can also be employed combining both free radical and cationic UV polymerization. Electron beam curable materials would also be appropriate for use in the presently disclosed methods. Electron beam formulations are similar to UV free radical systems but do not require the presence of free radicals to initiate the curing process. Instead the curing process is initiated by high energy electrons.

Preferably the finished pattern is visible (optionally after magnification) to the human eye and so advantageously the curable material comprises at least one colourant which is visible under illumination within the visible spectrum. For instance, the material may carry a coloured tint or may be opaque. The colour will be provided by one or more pigments or dyes as is known in the art. Additionally or alternatively, the curable material may comprise at least one substance which is not visible under illumination within the visible spectrum and emits in the visible spectrum under non-visible illumination, preferably UV or IR. In preferred examples, the curable material comprises any of: luminescent, phosphorescent, fluorescent, magnetic, thermochromic, photochromic, iridescent, metallic, optically variable or pearlescent pigments. The second curable material may be the same as the first curable material but could differ from the first curable material in one or more properties such as curing agent or colour.

In this specification, by "curable", we mean that the material hardens (i.e. becomes more viscous and preferably solid) in response to exposure to curing energy which may for example comprise heat, radiation (e.g. UV) or an electron beam. The hardening involves a chemical reaction such as cross-linking rather than mere physical solidification, e.g. as is experienced by most materials upon cooling.

The material of the transfer member must be chosen so that the curing radiation can travel through it. A typical example is quartz which is substantially transparent to UV radiation but other suitable materials include any polymer film which is transparent to ultraviolet in the wavelength range suitable for free radical or cationic UV polymerisation, this is typically within the wavelength range 200-400nm. Acrylic based polymer films are a typical material for this application. The transfer member could be planar but in order to minimise the use of space, is preferably fully or partially tubular and in the most preferred embodiments comprises a cylinder.

Step (e) typically comprises generating curing radiation at a location facing the second surface or conveying curing radiation to a location facing the second surface from a remote source.

In some embodiments, the portions of the transfer member cured in step (e) are removed after completion of step (h) using a doctor blade or the like.

In other embodiments, however, the method further comprises during step e), bringing a second substrate in contact with the transfer member while curing the pattern support layer, and then separating the second substrate the transfer member whereby the cured pattern support layer transfers onto the second substrate. In these embodiments, the cured portions of the pattern support layer are removed before step (f) and indeed provide a high resolution complementary image on the second substrate which could be used for another application such as a micro-optic application, high resolution security patterning etc. If the first substrate is transparent or translucent to suitable curing radiation, then step (g) could be accomplished by causing curing radiation to be transmitted through the first substrate to reach the uncured, pattern support layer. On the other hand, if the first substrate does not allow curing radiation to be transmitted through it, for example if the substrate has a metal surface, then step g) comprises causing curing radiation to impinge on the pattern support layer without passing through the first substrate.

Typically, the first substrate is a metal or has a metal surface onto which the cured materials are transferred in step (h). In alternative embodiments, the first substrate comprises a polymer which is preferably transparent or translucent in the visible, at least in the region of the cured first curable material. This then ultimately allows the image defined by the cured first curable material to be viewed through the first substrate.

Where the substrate has a metal surface, preferably the method further comprises subsequent to step h), removing metal from those areas of the substrate that are not provided with transferred, cured first and second curable materials. This could be achieved by passing the substrate through a caustic bath or using any other known demetalising technique.

The effect of this is that a very high resolution de-metallised image can be produced which has not previously been possible. As mentioned above, the printed product is particularly suitable for use in a security device and although microimages produced in this way could be used by themselves, preferably, the method further comprises providing optical focusing or optical magnifying elements on one or both sides of the substrate. As it is explained above, the optical focusing or optical magnifying elements may comprise microlenses, for example spherical or cylindrical microlenses.

The optical focusing or optical magnifying elements can be applied onto the first substrate using any conventional technique such as a cast cure process as known in the art.

In some examples, the optical focusing or optical magnifying elements are provided on one side of the first substrate, typically on the opposite side to the cured first curable material. In other cases, the optical focusing or optical magnifying elements are provided on both sides of the first substrate, the first substrate being transparent or translucent, and wherein typically the first and second curable materials have different colours so that different optical effects are visible when the result in the security device is viewed from each side. In preferred aspects of the invention, the optical focusing or optical magnifying elements cooperate with the microimages to generate an optically variable effect such as one of moire magnification, integral imaging, and a lenticular effect. Typically, the printed product can be used as part of a security document such as one of a banknote, cheque, identification document, passport, visa or stamp. However, the printed product could also be used in the form of a security article such as a thread, strip, patch, file or insert which is incorporated into or applied onto any security document.

Some examples of methods and apparatus according to the invention will now be described with reference to the accompanying drawings in which:-

Figure 1 is a schematic side view of apparatus for producing a printed product according to a first embodiment of the invention;

Figure 2 is a view similar to Figure 1 but of apparatus for producing a printed product according to a second embodiment of the invention; Figure 3 is a side view of the apparatus of Figure 1 in line with a de-metallisation system;

Figure 4 is a side view of the apparatus of Figure 1 in line with a cast cure process for adding micro focusing optical elements;

Figure 5 is a side view of the apparatus of Figure 3 further in line with apparatus for applying micro focusing elements; and,

Figure 6 is a side view of the apparatus of Figure 3 in line with two systems for applying micro focusing elements on opposite sides of the substrate.

The apparatus shown in Figure 1 comprises a cylindrical transfer member 1 having an outer, first surface 2 and an inner, second surface 3. In this example, the transfer member is made of quartz which allows UV radiation to pass through. The transfer member 1 has been micro engraved to produce an array of recesses 4 in the outer surface 2 defining a desired image array.

In use, the cylindrical, transfer member 1 is rotated in an anti-clockwise direction as shown by an arrow 5.

At a first station 10, an ink supply roller 11 is provided which rotates in an anticlockwise direction 12 and is supplied with a UV curable ink 13 in a conventional manner from a source (not shown). As the transfer member 1 and the supply roller 11 rotate, ink 13 is transferred into the recesses 4 in the transfer member 1.

As can be seen in Figure 1 , although the ink 13 will also coat the surface 2 of the transfer member adjacent the recesses 4, a doctor blade 14 removes the excess ink so that the ink is only present in the recesses.

The filled recesses 4 then move to a curing station 20 upon rotation of the member 1. The ink 13 contains a UV absorber and the curing station 20 is provided with a UV source 21 which generates UV radiation 22 that impinges on the ink 13 in the recesses 4 when they are present in the curing station 20. The ink is then fully cured in the recesses.

As noted above, there are many modifications of this process and for example there could be a sequence of applications of the same or different ink 13 with a final curing stage or with a curing stage after each application of ink.

The cured ink in the recesses 4 is then moved upon rotation of the transfer member 1 to a pattern support layer application station 30. This station 30 includes an application roller 31 onto the surface of which is applied (from a source not shown) a layer of a second curable material 32. The roller 31 rotates in an anti-clockwise direction 33 and deposits a layer of the second curable material as a pattern support layer 34 onto the surface 2 of the transfer member 1. As can be seen in Figure 1 , the pattern support layer 34 extends fully over the surface 2 of transfer member 1 including over the cured material 13 in the recesses 4. These materials are then brought to a further curing station 40 which includes a UV source 41 located inside the transfer member 1. UV radiation 42 from the source 41 is guided radially outward and impinges on the internal surface 3 of the transfer member 1. Since the transfer member 1 is made of quartz, the UV radiation will pass through the wall of the transfer member but any radiation impinging on the wall of the transfer member defining recess 4 will not pass through the cured ink 13 because the ink contains a UV absorbing pigment or an absorbing additive.

Examples of suitable UV absorbing additives/pigments include:- - Any of the hydroxyphenylbenzotriazole class of materials including :

a) Phenol, 2-(5-chloro-2H-benzotriazol-2-yl)-6-(1 ,1 -dimethyl)-4-methyl- eg. CIBA TINUVIN 326

b) 2-(2-hydroxyphenyl)-benzotriazoles

c) 2-hydroxy-benzophenones

d) hydroxyphenyl-s-triazines

e) oxalanilides

• Titanium dioxide (White in appearance) / Nano- Titanium Dioxide (Transparent in appearance)

- Carbon Black

An example formulation of a suitable ink is:

- 20 wt% titanium dioxide

• 60 wt% Epoxy acrylate resin

15 wt% monomer viscosity modifier

- 5 wt% photo initiator

Thus, the corresponding part 34A of the pattern support layer aligned with the ink 13 will not be cured. It will also be noted that the uncured portions 34A are thus self-registered with the recesses 4. On the other hand, the radiation will pass through those regions of the transfer member 1 circumferential ly offset from the recesses 4 and cure the corresponding portions 34B of the pattern support layer 34. It will be seen therefore that the cured material 13 in the recesses 4 acts as a mask to prevent the passage of UV radiation therethrough.

The transfer member 1 continues to rotate to bring the materials to a final transfer station 50. In this example, a transparent (to visible and UV) polymer substrate 51 is urged into contact by a pressure roller 52 with the transfer member 1. At the same time, UV radiation 53 from a source 54 passes through the substrate 51 and is irradiated onto the pattern support layer 34. When uncured regions 34A of the support layer 34 receive the radiation, they are cured and at the same time adhere to the substrate 51. On the other hand, the previously cured portions 34B of the pattern support layer 34 are unaffected. As the transfer member 1 continues to rotate, the adhered portions 34B remain adhered to the substrate 51 and to the ink portions 13 and thus draw out the portions 13 as shown at 55. These drawn out portions thus define the desired microimage array on the substrate 51.

The portions 34B of the pattern support layer remain adhered to the transfer member 1 and are removed by a doctor blade and/or chemical bath 60.

The result of this process is the provision of a high resolution microimage array on the substrate 51 which can then be used in a variety of applications as will be described further below.

Typically, the second curable material 32 will be colourless so as not to affect the colour of the intaglio ink 13. However, it is also possible for the second curable material 32 to have a colour which may combine with the colour of ink 13 in a desired manner or indeed both colours could be opaque so that the product appears in the colour of the ink 13 when viewed from above and in the colour of the ink 32 when viewed from below through the substrate 51. The embodiment shown in Figure 2 is similar to that shown in Figure 1 as far as stations 10, 20 and 30 are concerned. These will therefore not be described again. The main difference with the Figure 1 embodiment is the modification of the station 40 to a pattern support layer removal station 40'.

The station 40' comprises a pressure roller 61 forming a nip with the transfer member 1 through which a second, polymer substrate 62 is fed.

In this embodiment, the portions 34B of the pattern support layer 34 are cured by radiation 42 while in contact with the second substrate 62, adhere to the second substrate 62, and are removed from the transfer member 1 at this position. There is therefore no need for a downstream doctor blade or other removal system 60.

The transfer member 1 then continues to rotate without the portions 34B to the transfer station 50 when portions 55 transfer onto the first substrate 51 as in Figure 1.

In the embodiments described above, the first substrate 51 was a transparent polymer material. The invention is particularly applicable for use with metalised substrates. Figure 3 illustrates the Figure 1 apparatus being used in conjunction with a substrate 100 formed by a polymer material 101 and a metal coating, such as aluminium, 102. The apparatus for producing the printed microimage array is almost exactly the same as that shown in Figure 1 and will not be described again. However, there is one exception. In view of the metalisation 102, the substrate 100 is not transmissive to UV radiation. As a result, the UV source 54 must be placed above the substrate 100 so that the UV radiation 53 is directed into the nip between the transfer member 1 and the substrate 100. Of course, the apparatus of Figure 2 could be utilised instead.

The printed substrate 100 is then passed into a caustic bath 110 which demetalises or removes the metal 102 between the printed image portions 55 (comprising ink portions 34A and 13) so that the final product has a de- metallised imagery of very precise register and high accuracy, for example up to 2 pm or even less. The metal provides a high opacity unachievable through print and therefore increases the colour strength of the inks. This would also produce a dual sided effect; ink visible from one side, metal from the other, perfectly registered.

Figure 4 illustrates an alternative application of the printed product. In this case, the apparatus producing the printed product is the same as that shown in in Figure 1 although of course it could be the same as in Figure 2.

In this application, the printed product is fed to a UV cast cure system 200 which applies linear microstructures such as microlenses 210 in a conventional manner in alignment with each printed element 120.

Of course, in the examples of Figures 3 to 6 one or both of the UV cast cure and caustic bath processes could be off-line as well as in-line. In the example shown in Figure 4, the microlenses 210 are provided on the opposite surface of the substrate 51 to the image element portions 55. This is particularly suitable for the formation of security devices such as moire magnifiers and the like. However, the lenses 210 could be provided on the same surface as the image elements 120. An example of this will be described later.

Figure 5 illustrates the example of Figure 3 but in which the de-metallised product is fed to a UV cast cure system 200 for the application of microlenses 210 in the same way as in the Figure 4 example. Again, the microlenses 210 could be on the opposite side (as shown) or the same side as the image element portions 55.

In the example of Figure 6, the printed product from the apparatus shown in Figure 1 (or Figure 2) is fed in-line and in-sequence to two cast cure systems 200, 300 so as to apply microlenses 210, 310 in register on opposite sides of the substrate 51.

In this case, the inks 13, 32 are chosen to have different colours, for example blue and green and to be opaque. This then produces a highly secure security device in the form of a dual sided, dual colour microlens feature in which the inks 13, 32 are in perfect register. Thus, the microimage 210 and image elements 55 could form a first lenticular device which is viewed from the side 400, the colour of the image being defined by the ink 32; while the microlenses 310 and the image elements 55 form a second lenticular device viewed from the side 410, defined by the colour of the ink 13.