Methods of manufacturing security devices

Abstract

A security device manufacturing method includes: providing a substrate having a viewing region; providing an obscuring layer in the region; providing a first image; applying a mask to the first image and swapping colour components of first and second sub-images of the first image forming: a mask pattern, and a background pattern representing the unswapped colour components on their assigned side; and printing the mask and background patterns on corresponding layer sides. The layer reduces colours visibility on one side when the other side of the layer is viewed in reflection, and allows light through the region when the security device is viewed in transmitted light. When either side of the region is viewed in reflected light, the patterns on that side are dominantly visible and may be distinguished. When the region is viewed in transmitted light from either side, the region is transparent and the colour-composite image is visible.

Claims

1. A method of manufacturing a security device, the method comprising: providing a substrate having a viewing region; providing an obscuring layer in the viewing region; providing a first image being a colour-composite image, the colour-composite image being formed of a first sub-image and a second sub-image, wherein: the first sub-image and the second sub-image are respectively formed of a first set of colour components and a second set of colour components, the first sub-image and the second sub-image are each initially assigned to one of two sides of the obscuring layer, and each of the first and second sub-images is not homogeneous; applying a mask representative of a second image to the first image; swapping colour components of the first and second sub-images of the first image at each location indicated by the mask, such that: the first set of colour components of the first sub-image is re-assigned from its initially assigned side of the obscuring layer to the other side at each location indicated by the mask, and the second set of colour components of the second sub-image is re-assigned from its initially assigned side of the obscuring layer to the other side at each location indicated by the mask, wherein the swapping of colour components results in, at each side of the obscuring layer, a mask pattern representing the swapped colour components, and a background pattern representing unswapped colour components; printing the mask and background patterns on their corresponding side of the obscuring layer; wherein the obscuring layer between the printed patterns reduces a visibility of colours on one side when the other side of the obscuring layer is viewed in reflection, the obscuring layer allowing light to pass through the viewing region when the security device is viewed in transmitted light, whereby: when the viewing region is viewed in reflected light from either side of the obscuring layer, the patterns on the viewed side of the obscuring layer are dominantly visible compared to the patterns on the other side, and the patterns on the viewed side are distinguished from each other at least by their respective colours to make the second image visible; and when the viewing region is viewed in transmitted light from either side of the obscuring layer, the viewing region is sufficiently transparent that colour mixing between overlapped different colours of the patterns on both sides of the obscuring layer results in the first image, which is the colour-composite image, being visible.

2. The method according to claim 1, wherein the first sub-image is assigned to one side of the obscuring layer, the second sub-image is assigned to the other side of the obscuring layer, and applying the mask to the colour-composite image results in forming the mask and background patterns respectively for printing on each side of the obscuring layer.

3. The method according to claim 1, wherein the colour mixing between the overlapped different colours is additive or subtractive colour mixing.

4. The method according to claim 2, wherein the mask patterns printed on either side of the obscuring layer are superimposed on and in register with one another.

5. The method according to claim 1, wherein the mask pattern defines indicia.

6. The method according to claim 1, wherein the mask pattern defines continuous blocks of respective colours or discontinuous regions.

7. The method according to claim 1, wherein the background pattern is ordered or homogeneous.

8. The method according to claim 2, wherein the mask pattern and the background pattern printed on one of the sides of the obscuring layer define solid areas of respective colours.

9. The method according to claim 1, wherein, when the security device is viewed in transmission, the resultant colour-composite image is a full colour-composite image representing an indicium, or symbol, alphanumeric character.

10. The method according to claim 1, wherein the patterns are printed on the substrate by one of lithography, UV cured lithography, intaglio, letterpress, flexographic printing, gravure printing, digital printing or screen-printing.

11. The method according to claim 1, wherein the patterns are printed using one or more of coloured inks, white inks, black inks, metallic inks, optically variable inks, and fluorescent inks.

12. The method according to claim 1, wherein printing is performed after the viewing region and obscuring layer have been provided to the substrate.

13. The method according to claim 1, wherein the obscuring layer is semi-transparent.

14. The method according to claim 1, comprising providing at least one opacity layer printed onto the viewing region.

15. The method according to claim 14, wherein the opacity layer is a third sub-image of the colour-composite image positioned at areas of the substrate to which the mask does not apply, and the third sub-image comprises a set of K colour components.

16. The method according to claim 14, wherein the opacity layer is the first sub-image of the colour-composite image, and the first sub-image comprises a set of K colour components.

17. The method according to claim 1, wherein transparency of the substrate varies over the viewing region.

18. The method according to claim 1, wherein the substrate comprises a transparent polymer provided with at least one layer of an opacifying coating, the viewing region being defined by omitting the opacifying coating in a localised region.

19. A security device comprising: a substrate having a viewing region; an obscuring layer in the viewing region; and mask and background patterns printed in the viewing region according to a mask applied to a first image being a colour-composite image, the colour-composite image being formed of a first sub-image and a second sub-image, wherein the first sub-image and the second sub-image are respectively formed of a first set of colour components and a second set of colour components, the first sub-image and the second sub-image are each initially assigned to one of two sides of the obscuring layer, and each of the first and second sub-images is not homogeneous; wherein the mask is representative of a second image and is applied to the first image; wherein colour components of the first and second sub-images of the first image are swapped at each location indicated by the mask, such that: the first set of colour components of the first sub-image is re-assigned from its initially assigned side of the obscuring layer to the other side at each location indicated by the mask, and the second set of colour components of the second sub-image is re-assigned from its initially assigned side of the obscuring layer to the other side at each location indicated by the mask, wherein each side of the obscuring layer includes: a printed mask pattern representing the swapped colour components, and a printed background pattern representing unswapped colour components; wherein the obscuring layer between the printed patterns reduces a visibility of colours on one side when the other side of the obscuring layer is viewed in reflection, the obscuring layer allowing light to pass through the viewing region when the security device is viewed in transmitted light, whereby: when the viewing region is viewed in reflected light from either side of the obscuring layer, the patterns on the viewed side of the obscuring layer are dominantly visible compared to the patterns on the other side, and the patterns on the viewed side are distinguished from each other at least by their respective colours to make the second image visible; and when the viewing region is viewed in transmitted light from either side of the obscuring layer, the viewing region is sufficiently transparent that colour mixing between overlapped different colours of the patterns on both sides of the obscuring layer results in the first image, which is the colour-composite image being visible.

20. An article of value comprising the security device according to claim 19, wherein the article of value is a security document, the security document comprising: banknotes, passports, ID cards, fiscal stamps, cheques, postal stamps, certificates of authenticity, articles used for brand protection, bonds, or payment vouchers, or wherein the article of value comprises: a bottle for a liquid, a container for a liquid, clothing, footwear, a consumer electronic product, cigarettes, a tobacco product, or a software product.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Some examples of security devices located on or in security documents according to the invention will now be described with reference to the accompanying drawings, in which:

(2) FIG. 1 is a flow diagram of a general method applicable to each example;

(3) FIGS. 2a and 2b are cross-sections through a first example of a security device;

(4) FIG. 3 is an illustration of the security device of the first example when viewed in reflection;

(5) FIGS. 4a-4c are plan views of a second example of a security device when viewed in reflection from opposite sides and in transmission respectively; and

(6) FIGS. 5a to 5c illustrate further examples of a security device according to the invention.

DESCRIPTION OF EMBODIMENTS

(7) We now describe a number of different examples of security devices applicable to security documents. Common to the production of each of these example security devices is a general method of forming the security devices and this is now firstly described in relation to FIG. 1.

(8) FIG. 1 is a flow diagram of the key stages in the process of forming such a security device. Initially, at step 100, a composite-colour image (Image 1) is chosen as the image to be viewed in transmission. When printed, the full-colour image may be represented, in this example, by the CMYK colour model. Accordingly, the colour-composite-image is formed of four sub-images, each having corresponding sets of colour components: cyan (C), magenta (M), yellow (Y), and black (K). Image 1 may be the image shown in FIG. 5c, for example.

(9) The colour components of Image 1 are split, so that they are each associated with either side of the obscuring layer to be printed on. By way of example, the Y component is to be printed on the front of the substrate comprising the obscuring layer, while the C, M, and K components are to be printed on the other side of a substrate 10, as shown for example in FIG. 2a. Although FIG. 2a shows only a small section of the device, where each of the colour components or channels is a homogeneous layer with no gaps between the colour components in either layer, layers are not homogeneous throughout the entire image. It will be appreciated that the number of the sub-images assigned to either side of the substrate may vary. For example, in a colour model with 4 colour components, the split numbers of sub-images either side may be 0/4, 1/3, 2/2, 3/1 or 4/0.

(10) Referring back to FIG. 1, the next step 200 is to provide an image to be viewed in reflection (Image 2) and a mask outlining this image. FIG. 3 illustrates an Einstein profile representing an example Image 2 when viewed in reflection. Next, Image 1 is processed to form Image 2 as is described with reference to steps 300 and 400 below. The mask pattern outlining Image 2 may represent continuous areas or blocks, or be discontinuous.

(11) At step 300, Image 1 is screened with the mask and at step 400, colour components either side are swapped inside the mask to form mask patterns, as schematically shown in the section of FIG. 2b. In this case, the C and M colour components of Image 1 are moved to the front of the substrate, while the Y colour component is moved to the back of the substrate, inside the mask. The order of the C and M colour components either side of the obscuring layer at each location does not matter.

(12) FIG. 3 shows an example of the device viewed in reflection from the front side of the viewing region, with the mask pattern (Einstein's profile) made up of the cyan and magenta colour components being perceived against a yellow background. The yellow background is dominant in reflection, being backed by an obscuring layer, included at step 500, as will be described below. Similarly, when the device is viewed in reflection from the back side of the viewing region, a yellow mask pattern (Einstein's profile) made up of the swapped yellow components will be viewed against a background pattern made up of the cyan and magenta colour components. It will be appreciated that, in practice, a faint outline of Image 1 (a residual image) may additionally be perceived by the user, as illustrated in FIG. 3.

(13) At step 500, an obscuring layer, also referred to as an opacifying layer 11,12 is provided to the substrate to be located between printed layers as shown in FIGS. 2a and 2b. In this case, the substrate is a transparent substrate 10 comprising an opacifying coating 11 on both sides of the substrate. It will be appreciated that the obscuring layer 12 may be provided one or both sides of the substrate anywhere between the printed layers. In some embodiments, the obscuring layer is a multi-layer (i.e. comprising two or more obscuring layers) and may comprise a K or thick white layer representing a K sub-image of the full-colour image. The mask may or may not be applied to the K sub-image. In particular embodiments, a K layer is provided between two opacifying layers located either side of the substrate, as shown in FIG. 2b. The K layer is not necessarily applied to the whole viewing region, and may be non-uniform.

(14) The obscuring layer is provided so that, in reflection, the colours on the side being viewed are dominant, and the effect of the colour on the opposite side of the substrate is negligible. In the case shown with reference to FIGS. 2b and 3, a yellow mask pattern is the dominant colour when the back side of the device is viewed in reflection, whilst a mask pattern of the colours resulting from a combination of cyan and magenta is dominant when the front side of the device is viewed in reflection. Similarly, a yellow background is dominant in reflection on the front side, whilst a cyan and magenta background is dominant in reflection on the back side. In transmission, the obscuring layer is sufficiently transparent to allow the result of the colour mixing of the colours of the component layers for Image 1 to be observed as a full colour composite, as shown in FIG. 5c, for example.

(15) At step 600, the patterns obtained following the processing of Image 1 at steps 300 are printed either side of the obscuring layer, on the front and back sides of the substrate in this example. The patterns either side of the viewing region may be printed simultaneously on the front and rear side of the viewing region using a conventional technique such as lithographic printing. Alternatively the front and rear side may be printed in-line using a process such as gravure. Preferably, the printing is performed after the viewing region and obscuring layer have been provided to the substrate.

(16) The use of an obscuring layer is known for conventional see-through features. A wide variety of materials could be used for the obscuring material but a good example for the present invention is the use of a K or thick white opacifying layer representing a K sub-image of the full-colour image which is not processed by the mask. Additionally or alternatively, the obscuring layer may comprise a vapour deposited metallic layer. For example the transparent substrate within the viewing region could be coated with a metallic material which is then partially demetallised to enable the feature to be viewed in transmitted light.

(17) The obscuring may be in the form of a screen. For example, the metallised pattern could be an array of dots or lines with sufficient coverage to maintain the reflectivity but sufficiently transparent to enable colour mixing of the colour component layers to be viewable in transmitted light. Non-linear screens are also envisaged. For example the screen could comprise a circular or sinusoidal array of dots or lines. The screen can be regular or stochastic. Indeed, the term screen should be construed broadly to encompass many different shapes of screen elements.

(18) Preferably, the overall transmission of the screen pattern (representing the percentage of light intensity transmitted through the screen) is in the range 20-80%, and more preferably in the range 40-70% and even more preferably in the range 50-70%. The width of the lines or the diameter of the dots forming the screen are preferably in the range 50-250 m and the spaces between the dots or lines are also in the range 50-250 m with values of each set chosen to achieve the desired screen coverage.

(19) The metallised pattern could be an array of dots or lines with sufficient coverage to maintain the reflectivity of the layers printed either side of the screen, but sufficiently transparent to enable colour mixing of the colour component layers to be viewable in transmitted light. This is particularly appropriate with a polymeric substrate. Alternatively, the substrate could be coated with a very thin film of aluminium, metal oxide or other reflective layer such that again it exhibits both high reflectivity and sufficient transparency. As an alternative to a vapour deposited metallic layer the obscuring layer could be formed by a printed metallic ink.

(20) Alternatively the obscuring layer can comprise a coat, such as Coates 3188XSN or Coates Heliovyl White S90 353 for example. A typical coat weight is suggested to be in the region of 1-3GSM. These coats are already commonly used in banknote security threads to conceal information in reflected light.

(21) In the case of a polymer document substrate such as a banknote the obscuring layer is preferably formed from the opacifying coating applied to the polymer substrate and will comprise a resin such as a polyurethane based resin, polyester based resin or an epoxy based resin and an opacifying pigment such as titanium dioxide (TiO2), silica, zinc oxide, tin oxide, clays or calcium carbonate.

(22) Two or more opacifying layers may be applied to each surface of the polymer substrate in order to achieve the necessary opacity. The optical density of each layer by itself may typically be around 0.1 to 0.5. Preferably, 3 or more layers are applied to each surface, overlapping one another.

(23) In a preferred embodiment, at least one of the opacifying layers (preferably one on each surface of the polymer substrate is made electrically conductive, e.g. by the addition of a conductive pigment thereto. This reduces the effect of static charges which may otherwise build up on the security document during handling.

(24) The opacifying layers are preferably applied to the polymer substrate using a printing process such as gravure printing, although in other case the opacifying layers could be coated onto the substrate, or applied by offset, flexographic, lithographic or any other convenient method. Depending on the design of the security document, the opacifying layers may be omitted across gaps on one or both surfaces of the polymer substrate to form window regions (which may be full windows or half windows, or a mixture of both). This can be achieved through appropriate patterning of the opacifying layers during the application process.

(25) In the present invention the obscuring layer of the viewing region may be formed by a thinner region of the opacifying coating compared to the rest of the polymer document substrate. For example in the viewing region a single layer of the opacifying coating may be applied on one side of the substrate whereas in the rest of the document three layers of the opacifying coating may be applied to each side of the substrate.

(26) The security document shown in the example of FIG. 4 comprises a substrate 10 which may be paper or polymer, in this case paper. The substrate 10 defines front and rear sides and has a substantially transparent viewing region 2. The substantially transparent viewing region 2 may have been formed using any of conventional methods.

(27) Printed on the front side of the viewing region 2 (FIG. 4a) is a first mask pattern 3 in colour A and a first background pattern 4 in colour B. In this example, the mask component 4 is in the shape of a star. It will be appreciated that the colours of the patterns printed on the front side may have one or multiple colour channels obtained by standard methods such as lithographic, gravure, screen or digital printing. In other words, colour A or colour B printed on the front side may represent one colour component if the full-colour image has a single colour component assigned to the front side, or may represent two or more colour components if the full-colour image has two or more colour components assigned to the front side. The split of the colour components of the full-colour image and the colours of the inks are preferably chosen to provide relatively high contrast between the regions defined by colours A and B when viewed in reflection.

(28) Printed on the rear side of the viewing region 2 is a second mask component 5 in colour B and a second background image component 6 in colour A. The second dot pattern 5 is the same as the first dot pattern 3 apart from the fact that the colours are now reversed such that colour A now forms the star shape 5 and colour B forms the background region 6.

(29) The second mask component 5 has the same shape as the first mask component 3 and is in substantially perfect register, being directly superimposed on the first mask component 3.

(30) When viewing the device in reflection from the front of the substrate the first mask pattern (star in Colour A) is observed against the first background in Colour B (FIG. 4a). Likewise when viewing the device in reflection from the rear of the substrate the second mask pattern 5 (star) is observed against a background in reversed colours from the front side (FIG. 4b). When viewing the device in transmission, from either side of the device, the coloured printed inks, a colour composite image 7 (having sets of colour components A and B split between both sides of the obscuring layer) is observed as a result of subtractive colour mixing. The distribution of the colour components within each colour component layer (with absence of colour components in a layer) is such that colour mixing between the overlapped patterns forms a pattern from a combination of Colour A and Colour B components. In this manner, the mask patterns (star shapes) disappear when viewed in transmission and are replaced with the full colour-composite image 7, as shown in FIG. 4c.

(31) FIG. 5a shows another example of a banknote 20 provided with a security device having a viewing region 22, viewed in reflected light. It may be seen that the banknote 20 comprises additional security devices as known in the art, some of them forming indicia. FIG. 5b is a close-up of the viewing region 22 viewed in reflection from the front side, with mask patterns representing lightbulbs. FIG. 5c shows the viewing region when viewed in transmission from either side of the device, showing the colour-composite image.