Patent Description:
Valuable documents, such as banknotes, shares, bonds, certificates, vouchers, checks, some highly coveted admission tickets, but also other documents that are susceptible to counterfeiting, such as passports or other identification documents, are generally provided with various security elements to increase their resistance to counterfeiting. The security elements can be designed, for example, in the form of security threads embedded in a bill, or an applied security strip or a self-supporting transfer element which is applied to a document of value after its production.

There are several well-known designs of the security elements, in the current state of the art. Such security elements are generally designed with multilayer thin-film elements, with their color impressions changing for the viewer changes with varying viewing angles. Some of the examples may include transition from green to blue, from blue to magenta or from magenta to green, etc. Such security elements with color changes when tilting/rotating and or translating the security elements are referred to as color shift effect security elements.

Color-shift effects can be obtained by various means, for example using thin-film interference by means of structures for example which have a layer that reflects electromagnetic waves, a spacer layer and a layer formed from metallic clusters. Another way of obtaining a security element which has a color-shift effect is to use a coating consisting of liquid crystals, either in the form of a pigmented layer or a polymerized film.

Though color shift security film are already known in the prior art, there is still a need to provide improved color shift security film which have better complexity, such that the color shift film changes color with viewing angle and is capable of exhibiting plurality of colors or dual color effect to prevent counterfeiting.

<CIT> discloses a security element with a front side and a back side opposite the front side, the security element having two or more security features, a first security feature of the two or more security features comprising one or more first layers and a second security feature of the two or more security features comprising one or more second layers. The first security feature and the second security feature are arranged in particular in register with one another, the first security feature generating at least one first optically variable effect and the second security feature generating at least one second optically variable effect, the at least one first optically variable effect has a first color and the at least one second optically variable effect has a second color, the first color and the second color differing from one another. A method for producing such a security element is also disclosed.

<CIT> discloses a security device comprising at least one cholesteric liquid crystal (LC) layer disposed on a substrate, the cholesteric LC layer collectively exhibiting an image detectable by the naked eye under non-polarised visible light illumination. The cholesteric LC layer has a respective pattern of one or more first regions of the layer in which the cholesteric LC is ordered and thereby exhibits an optically variable visible colour, alongside one or more second regions of the layer in which the cholesteric LC is disordered and thereby is substantially transparent and colourless in the visible spectrum. The combination of the one or more respective patterns forms the image. There is also provided a security device component comprising a plurality of curable cholesteric LC layers disposed on the substrate, each formed of a different radiation curable cholesteric LC material and exhibiting an optically variable visible colour, wherein when viewed at a predetermined viewing angle, the visible colour exhibited by each one of the cholesteric LC layers is different from that of the other cholesteric LC layer(s). Some of the different radiation-curable cholesteric LC materials comprise respective photo-initiators which are responsive to different wavelengths of radiation.

The primary object of the present invention is to provide a security film with dual color shift characteristics.

Another object of the present invention is to provide a security film with dual color shift characteristics that provides enhanced design complexity that facilitates enhanced protection against counterfeiting.

Yet another object of the present invention is to provide a security film with dual color shift characteristics that exhibits plurality of colors or dual color effect to prevent counterfeiting.

Yet another object of the present invention is to provide several technically and/or commercially advantageous embodiments of the security film with dual color shift characteristics.

Yet another object of the present invention is to provide methods of manufacturing the security film with dual color shift characteristics.

According to a first aspect of the present invention, there is provided a security film with dual color shift characteristics, the security film comprising a substrate layer having a first substrate surface and a second substrate surface, a first liquid crystal layer, including a first liquid crystalline material, disposed above the first substrate surface, and a second liquid crystal layer, including a second liquid crystalline material, disposed above the second substrate surface. The security film further comprises an opaque black reflective coating between the first liquid crystal layer and the first substrate surface, wherein the reflective coating includes a plurality of metalized zones and a plurality of demetalized zones. The first liquid
crystal layer and the second liquid crystal layer are adapted to exhibit distinct color shifts, on rotation and/or translation of the security film.

In one embodiment of the invention, the security film comprises a reflective coating between the first liquid crystal layer and the first substrate surface.

In one embodiment of the invention, the reflective coating includes a plurality of metalized zones and a plurality of demetalized zones.

According to a second aspect of the present invention, there is provided a method according to claim <NUM>.

In one embodiment of the invention, the manufacturing of the security film includes combining a first set of layers with a second set of layers, such that, the first set of layers includes the substrate layer, the reflective coating provided onto the first substrate surface, the reflective coating undergo drying process, and the first liquid crystal layer provided onto the reflective coating, and the second set of layers includes a second substrate layer having a third substrate surface and a fourth substrate surface, and the second liquid crystal layer provided onto the fourth substrate surface. The first set of layers and the second set of layers have been manufactured independently. The first set of layers is combined with the second set of layers by joining an exposed surface of the second liquid crystal layer to the second substrate surface, in a manner, that the third substrate surface is facing the ambient. Also, the second substrate layer is removed to yield the security film, after combining the first set of layers with the second set of layers.

In the context of the specification, the phrase "high security paper" refers to value documents such as bank notes, bonds, bills, internal organizational memorandums, circulars, confidential documents, passports or other identification documents that are usually provided with various security elements to ensure their integrity and increase the protection against forgery.

So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may have been referred by embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. These and other features, benefits, and advantages of the present invention will become apparent by reference to the following text figure, with like reference numbers referring to like structures across the views, wherein:.

While the present invention is described herein by way of example using embodiments and illustrative drawings, those skilled in the art will recognize that the invention is not limited to the embodiments of drawing or drawings described, and are not intended to represent the scale of the various components. Further, some components that may form a part of the invention may not be illustrated in certain figures, for ease of illustration, and such omissions do not limit the embodiments outlined in any way. It should be understood that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the scope of the present invention as defined by the appended claim. As used throughout this description, the word "may" is used in a permissive sense (i.e. meaning having the potential to), rather than the mandatory sense, (i.e. meaning must). Further, the words "a" or "an" mean "at least one" and the word "plurality" means "one or more" unless otherwise mentioned.

Furthermore, the terminology and phraseology used herein is solely used for descriptive purposes and should not be construed as limiting in scope. Language such as "including," "comprising," "having," "containing," or "involving," and variations thereof, is intended to be broad and encompass the subject matter listed thereafter, equivalents, and additional subject matter not recited, and is not intended to exclude other additives, components, integers or steps. Likewise, the term "comprising" is considered synonymous with the terms "including" or "containing" for applicable legal purposes. Any discussion of documents, acts, materials, devices, articles and the like is included in the specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention.

In this disclosure, whenever a composition or an element or a group of elements is preceded with the transitional phrase "comprising", it is understood that we also contemplate the same composition, element or group of elements with transitional phrases "consisting of", "consisting", "selected from the group of consisting of, "including", or "is" preceding the recitation of the composition, element or group of elements and vice versa.

The present invention is described hereinafter by various embodiments with reference to the accompanying drawing(s), wherein reference numerals used in the accompanying drawing(s) correspond to the like elements throughout the description. This invention may, however, be embodied in many different formsand should not be construed as limited to the embodiment set forth herein. Rather,the embodiment is provided so that this disclosure will be thorough and completeand will fully convey the scope of the invention to those skilled in the art. In the following detailed description, numeric values and ranges are provided for variousaspects of the implementations described. These values and ranges are to betreated as examples only, and are not intended to limit the scope of the claims. Inaddition, a number of materials are identified as suitable for various facets of the implementations. These materials are to be treated as exemplary, and are not intended to limit the scope of the invention.

The present invention discloses security films with at least two liquid crystal layers disposed on two opposing surfaces of a substrate, at least one liquid crystal layer on each one of the two opposing surfaces. The liquid crystal layers are envisaged to exhibit dual color shifts, thereby providing enhanced resilience to the security film against counterfeiting. The visibility of the color shifts of one or both of the two liquid crystal layer may be enhanced by use of reflective coatings provided between the substrate and the liquid crystal layers. Additional security features may be incorporated by, either through etching or through deposition of material, in form of predesigned indicia, such as logos, numerals, emblems and signatures etc., of or on the reflective coating.

Also disclosed are several embodiments of methods for manufacturing of the aforementioned security films. In that manner, the methods for manufacturing are disclosed to include layer by layer attachment of the several layers of the security films, joined with each other through adhesives and/or thermal curing. Moreover, the security film may be manufactured by attaching two or more sets of layers that have been manufactured independently, thereby imparting modularity and design flexibility to the security film. Referring to the drawings, the invention will now be described in more detail.

<FIG> illustrates an exploded view of a security film <NUM>with dual color shift characteristics (hereinafter referred to as "the security film <NUM>"), in accordance with an embodiment of the present invention. <FIG> illustrates a cross-sectional view of the security film <NUM> of <FIG>. As illustrated in <FIG> and <FIG>, the security film <NUM>includes a substrate layer <NUM> having a first substrate surface <NUM> and a second substrate surface <NUM>. A first liquid crystal layer <NUM> has been disposed above the first substrate surface <NUM>. The first liquid crystal layer <NUM> includes a first liquid crystalline material. The first liquid crystalline material may include one or more of cholesteric liquid crystals, nematic liquid crystals, and combinations thereof. A second liquid crystal layer<NUM>, including a second liquid crystalline material, has been disposed above the second substrate surface<NUM>(on inverting the substrate layer <NUM> to expose the second substrate surface <NUM> to an operator or process equipment). The second liquid crystalline material may also include one or more of the cholesteric liquid crystals, the nematic liquid crystals, and combinations thereof.

It is further envisaged that the first liquid crystal layer <NUM> and the second liquid crystal layer <NUM> are adapted to exhibit dual color shifts, on rotation and/or translation of the security film <NUM>. Optionally, the first liquid crystal layer <NUM> and the second liquid crystal layer <NUM> may exhibit transition from any one color to any other color.

In that manner, a user will have dual verification of the integrity of a high security paper to which the security film <NUM> has been employed. In several embodiments, the substrate layer <NUM> may made from an industrial polymer such as Polyethylene Terephthalate (PET), and the first <NUM> and the second <NUM> liquid crystal layers may be attached to the substrate layer <NUM> with the use of adhesives.

<FIG>Cillustrates an exploded view of the security film <NUM>, in accordance with another embodiment of the present invention. <FIG>illustrates a cross-sectional view of the security film <NUM>of <FIG>. As illustrated in <FIG> and <FIG>, the security film <NUM> also includes a reflective coating <NUM> between the first liquid crystal layer <NUM> and the first substrate surface <NUM>. The reflective coating <NUM>, in several embodiments, is envisaged to be at least partially opaque in nature, in order to reflect light falling on the reflective coating <NUM>. Further, the reflective coating <NUM> is envisaged to be made from a metal selected from a group consisting of Aluminum, Silver, Nickel, Platinum, Palladium, and other highly reflective metals. In several embodiments, although not bindingly, Aluminum and/or Silver may be metals of choice owing to their widespread availability and relatively low fusion temperatures. In an embodiment of the present disclosure, the first substrate surface <NUM> is first opaque black coated by coating with a plurality of metalized zones<NUM>and a plurality of demetalized zones<NUM>. In addition, the opaque black coating forms the reflective coating <NUM>. In another embodiment of the present disclosure, the first substrate surface <NUM>is coated with any other coating, which is opaque in nature. In another embodiment of the present disclosure, the first substrate surface <NUM> is directly coated with the first liquid crystal layer <NUM>.

In several embodiments of the present invention, the reflective coating <NUM> may include the plurality of metalized zones <NUM> and the plurality of demetalized zones <NUM>. The plurality of demetalized zones <NUM> may be created by removal or substitution of metals from certain regions of the reflective coating <NUM>, through etching or through deposition of fused non-metallic or polymeric materials on the regions of interest. Such regions in the reflective coating <NUM> may be representative on identifiable indicia such as logos, emblems, alphanumeric characters, design patterns and signatures, etc. In an embodiment of the present disclosure, the reflective coating <NUM> consisting of metalized and demetalized zone undergo drying process. In an embodiment of the present disclosure, the second substrate surface <NUM>is directly coated with the second liquid crystal layer <NUM>. In an embodiment of the present disclosure, the first liquid crystal layer <NUM> may exhibit transition from blue to green color, when the security film <NUM> is tilted along a longitudinal axis, while the second liquid crystal layer <NUM> may exhibit transition from blue to magenta or magenta to green color. In addition, the first liquid crystal layer <NUM> and the second liquid crystal layer <NUM> facilitate dual color characteristics. In another embodiment of the present disclosure, the first liquid crystal layer <NUM> and the second liquid crystal layer <NUM> may exhibit transition from any one color to any other color.

It is also further envisaged, as characterizing aspects of the present invention, that methods for manufacturing of the security film <NUM> may also be disclosed. The methods disclosed in the following discussion are envisaged to be simple and inexpensive in implementation, easily scalable, divisible within several manufacturing facilities or within several process lines within a single manufacturing facility, while also being able to be easily integrated in a single process line with the single manufacturing facility. Further, the methods of manufacturing disclosed are envisaged to deploy easily available raw materials and existing infrastructure. In an example, the security film <NUM> is inserted in valuable documents, one side of the valuable document, when tilted or viewed in different angle, may change color from blue to green, whereas another side of the valuable document, when tilted may change color from blue to magenta or from magenta to green. In addition, results in providing an improved color shift security film with improved complexity.

<FIG> illustrates a method <NUM>for manufacturing the security film <NUM>, in accordance with an embodiment of the present invention. The method <NUM> begins at Step202, where the substrate layer <NUM> having the first substrate surface <NUM> and the second substrate surface <NUM> is provided. At Step <NUM>, the first liquid crystal layer <NUM> is attached onto the first substrate surface <NUM> using an adhesive. Also, at Step <NUM>, the second liquid crystal layer <NUM> is attached onto the second substrate surface <NUM>. As stated above, the first liquid crystal layer <NUM>and the second liquid crystal layer <NUM>are adapted to exhibit dualcolor shifts to prevent counterfeiting, on rotation and/or translation of the security film<NUM>.

<FIG> illustrates the method <NUM>for manufacturing the security film <NUM>,in accordance with another embodiment of the present invention. As illustrated in <FIG>, after Step <NUM>, the method <NUM> moves to Step <NUM>. At Step <NUM>, the reflective coating <NUM> is provided onto the first substrate surface <NUM> through the use of adhesives. The reflective coating <NUM> is located between the first liquid crystal layer <NUM> and the first substrate surface <NUM>. Further, at Step <NUM>, it is confirmed if there are predetermined indicia available to be provided in or on the reflective coating <NUM>. If the predetermined indicia are actually available, the method <NUM> moves to Step <NUM>, where predetermined zones of the reflective coating <NUM> are demetalized in accordance with the predetermined indicia. The demetalizing step causes the generation of the plurality of metalized zones <NUM> and the plurality of demetalized zones <NUM> in the reflective coating <NUM>.

Either following Step <NUM> or Step <NUM>, the method <NUM> moves to Step <NUM>. At Step <NUM>,the reflective coating <NUM> undergo drying process. At Step <NUM>, the first liquid crystal layer <NUM> is provided onto the reflective coating <NUM>, with the use of adhesives. At Step <NUM>, the second liquid crystal layer <NUM> is deposited onto the second substrate surface <NUM>, thereby resulting in the security film <NUM>. However, in several embodiments, as discussed below, the security film <NUM> may be manufactured by combining two or more independently manufactured sets of layers, thereby resulting in the security film <NUM>.

<FIG> illustrates the method <NUM>for manufacturing the security film <NUM>,in accordance with yet another embodiment of the present invention. <FIG> illustrates a graphical representation of the method 200of <FIG>. The method <NUM> as depicted through <FIG> and <FIG> involves combination of a first set of layers <NUM> with a second set of layers <NUM>. The first set of layers <NUM>, in that regard, includes the substrate layer <NUM>, the reflective coating <NUM> provided onto the first substrate surface <NUM>, the reflective coating <NUM> undergo drying process, and the first liquid crystal layer <NUM> provided onto the reflective coating <NUM>. The first set of layers <NUM> is generated by following Steps202, <NUM>, <NUM>, <NUM> (Optionally), <NUM>, and <NUM>.

For generation of the second set of layers <NUM>, at Step232, a second substrate layer <NUM> having a third substrate surface <NUM> and a fourth substrate surface <NUM> is provided. In several embodiments of the invention, the second substrate layer <NUM> is also made up of PET or any other industrial grade polymeric material. At Step <NUM>, the second liquid crystal layer <NUM> is provided onto the fourth substrate surface <NUM>, by bonding through adhesives. At Step236, the first set of layers <NUM> is combined with the second set of layers <NUM> by adhesion of an exposed surface of the second liquid crystal layer <NUM> to the second substrate surface <NUM>, in a manner, that the third substrate surface<NUM> is facing the ambient. At Step <NUM>, after combining the first set of layers <NUM> with the second set of layers <NUM>, the second substrate layer <NUM> is removed to yield the security film <NUM>.

Claim 1:
A security film (<NUM>) with dual color shift characteristics, the security film (<NUM>) comprising:
a substrate layer (<NUM>) having a first substrate surface (<NUM>) and a second substrate surface (<NUM>);
a first liquid crystal layer (<NUM>), including a first liquid crystalline material, disposed above the first substrate surface (<NUM>);
a second liquid crystal layer (<NUM>), including a second liquid crystalline material, disposed above the second substrate surface (<NUM>); and
a reflective coating (<NUM>) between the first liquid crystal layer (<NUM>) and the first substrate surface (<NUM>), wherein
the first liquid crystal layer (<NUM>) and the second liquid crystal layer (<NUM>) are adapted to exhibit dual color shifts to prevent counterfeiting, on rotation and/or translation of the security film (<NUM>),
characterised in that:
the reflective coating is an opaque black reflective coating and in that the reflective coating (<NUM>) includes plurality of metalized zones (<NUM>) and a plurality of demetalized zones (<NUM>).