WO2020217254A1

WO2020217254A1 - Robust colour shift security film with wide spectrum complex spectral values and security thread made therefrom

Info

Publication number: WO2020217254A1
Application number: PCT/IN2020/050372
Authority: WO
Inventors: Shilpan Patel; Rishil PATEL
Original assignee: Shilpan Patel; Patel Rishil
Priority date: 2019-04-20
Filing date: 2020-04-20
Publication date: 2020-10-29
Also published as: WO2020217254A8; WO2020217254A9; EP3959081A1

Abstract

The invention discloses a robust colour shift security film with more complex and consistent spectral values, for manufacturing high security thread for further insertion into high security substrates, like bank note paper.

Description

TITLE: ROBUST COLOUR SHIFT SECURITY FILM WITH WIDE SPECTRUM COMPLEX SPECTRAL VALUES AND SECURITY THREAD MADE THEREFROM.

FIELD OF INVENTION

The present invention relates to a cost effective, eco-friendly, high security film with enhanced spectrum wavelength and stable colour shift. More particularly the present invention discloses a high security colour shift film with more advanced way of making a high security film with colour shift effect that is far more stable and is more consistent its characteristics during the manufacturing process.

BACKGROUND OF THE INVENTION:

In general terms, security film with colour shift visual effects, give special security effects to a security threads, which are used for high secure materials such as banknotes, confidential paper, stamp paper and other application are made from conventional process which affects the quality and characteristics of the colour shift film due to repetition of process. The supply source of key raw materials also add to the security element, like in this case the LC and certain coatings are key raw materials.

Deficiencies in currently available colour shift threads has left banks and other security agencies grappling with problems such as:

a. Rubbing off or dulling of colour shift properties which is more scratch resistant and effectively repels sebum or dirt, during normal usage of currency in circulation.

b. Chemical and physical properties could not withstand in harsh environment during the circulation of currency

c. Deficiency in mechanical properties, like internal bonds breaking down due to external environments, thus leading to“debonding” of the liquid crystals from the laminated substrates due to partial or total de- lamination and giving a “false-positive” during the process of examination of this vital security feature of a bank note

d. Wider Variety of Colour Shift combinations— as present vacuum metallisation process or sputter technology has limitations of various metals or selected inorganic materials which can be evenly and consistently sputtered, throughout the web in a vacuum controlled chamber.

As mentioned above, the prior art has inherent problems, like the colour shift elements, being fragile, failing certain tests, like crumpling tests and rub tests, which is much required for long term useage during currency in circulation, and tend to give a“false positive” as far as security is concerned. This may be seem to happen, leading to the bond between the base film and the colour shift liquid crystals, like case, of certain prior art as mentioned in patent WO-A-03061980 or other inorganic particles (in case of vacuum metallization), as disclosed in Patent W02005038136A, being apolar chemicals, tend to get“unstuck” from the carrier PET film as these particles or coatings are fragile micro particles, but are responsible for the colour shifting effect, due to light interference, as explained in these disclosures -

Patent US 8603615B2 teaches about use of various inorganic particles being deposited on a carrier film. US 8603615B2 teaches the complexities of stacks, using inorganic materials like Tin Oxide, Silicon Oxide, etc, which reflect a different set of colours. Finding a combination which display a precise colour shift spectral value, and in particular a wide spectrum colour shift values, is very complex, never attempted by anyone in prior art, and an expensive operation, which may not be commercially viable, and therefore our invention teaches the wide spectrum colour shift values, using LC Films and combination thereof.

Similarly, in case of film being liquid crystal coated on clear PET film, has their own set of problems. As the carrier film and liquid crystal coating, being apolar has a weaker bond, as the same has been designed to release cleanly off the detachable carrier, during subsequent process of lamination on to the main substrate (Receiver film). A security thread made using this process, tends to lose its sheen and therefore the colour shift effect, during the currency in circulatio Product made using this processisalso costly process, and is not very environment friendly as the released donor film ends up as waste.

Liquid crystal materials can be incorporated into security devices either as a film, as for example in WO-A-03061980, or in the form of an ink as a liquid crystal in an organic binder, as for example in EP-A- 1156934. The advantage of a liquid crystal ink is that it can be applied using conventional gravure or roll to roll printing processes and therefore it is relatively straightforward to apply the liquid crystal material in the form of a design. However, the colour shift spectral value consistency, brightness and sharpness of the observed colour and colour-shift are significantly degraded for a liquid crystal ink compared to a liquid crystal film, as disclosed in our invention. This degradation is due to the variability in alignment of the cholesteric helical axis between the individual liquid crystals compared to the uniform alignment of the liquid crystal film.

Our invention protects the colourshift values and properties, by disclosing a robust colourshift film which displays consistent spectral values throughout the circulation life of the bank note, and laminating this unique LC film onto the main “receiver” substrate, which may be mettalised, demetalised, opaque/black printed or otherwise treated to display the desired colourshift spectral values.

In another embodiment, our invention discloses incorporating a tie coat onto the “receiver” substrate, which may be mettalised, demetalised, opaque/black printed or otherwise treated to display the desired colourshift spectral values and overcoating the same with a lacquer coating, having high gloss, scratch resistant, sebum resistant, dirt resistant and UV protective property. This coating may be engineered as per the specification of the end user, and is by no way to be a limitation. To protect the inherent properties of LC polymer during drying and curing process of LC film(s), our invention also discloses a robust overcoat, like but not limited to, a clear, UV curable lacquer to be used to protect the robustness of the colour shift qualities. This process includes a lacquer coating, having high gloss, scratch resistant, sebum resistant, dirt resistant and protection from long range nanometer (as found in daily sunlight) UV light. This coating may be engineered as per the specification of the end user, and is by no way to be a limitation.

Yet another way of making the security threads is to print/coat a web of clear film, preferably polyester film, with a specific colour shift ink/coating medium, on a metalized/de-metalized, optionally opaque printed/coated. To protect the fragile colour shift elements, there may be a necessity to embed the coating on one or both sides of the web with organic chemistry, to ensure much needed endurance and increase the robustness of the structure, once converted into a security thread or inserted into a banknote paper.

However, the prior art has following short comings:

1. The resultant colour shift coating of LC loosely adhesion to the carrier polyester film, as LC polymeric films are apolar and get disturbed easily, thus losing its colour shift properties when subjected to mechanical or chemical stress .

2. The complexity of colourshift was limited to a simpler algorithm of bifurgence and therefore may not be considered as high secure as these LC coating were formed into a single layer of chiral, nematic/cholestric combination eg; Blue to Green on the range of“VIBGYOR” .

3. Mechanical, chemical and physical properties could not withstand in harsh environment during the wide circulation of currency.

The process(es) as shown in prior art have several flaws, including less endurance, during the process of currency circulation and certain tests, like solvent resistance or laundry tests, which are normally specified by various governments, this print/coat process ends up losing its sheen, properties or security features, in short time, and thus creating security issues.

In order to overcome the aforementioned drawbacks faced by the prior art cited, there is a need to provide an improved security film that displays a robust and wide spectrum colour shift security film with more complex and consistent spectral values, displaying a wider spectrum of colourshift effect having a wider colour shift spectrum like, but not limited to, Blue (450nm +/- 15 nm) to Red (700 nm +/- 15 nm) that is more difficult to replicate and control by the fraudster, and cannot be scanned nor digitally printed. The disclosure of tie coat between the two LC films and between the LC film and the protective film will give robustness and longer life to the subsequent manufacture of high security thread after insertion into high security substrates, like bank note paper

OBJECT OF THE INVENTION:

The primary object of this invention relates to a robust, cost effective, eco- friendly, high security film with enhanced spectrum wavelength and stable colour shift.

Another objective of the present invention there is to provide a more complex, secure and an improved security film that displays a wider spectrum of colour shift effect like, but not limited to, Blue (450nm +/- 15 nm) to Red (700 nm +/- 15 nm) that is more difficult to replicate, thus creating a very secure currency note.

Another objective of the present invention is to provide an improved security film that is nearly transparent, clear to look at, but once overlaid on a dark/opaque substrate/indicia/text then it displays pre-defined set of colour, with precise spectral values having a complex colour spectrum when viewed at certain angles.

Yet another objective of the present invention is to provide a robust and improved Liquid Crystal polmer coated security film, which is further enhanced by a compatible tie coat. Yet another objective of the present invention is to provide a robust and improved Liquid Crystal polymer coated security film, which is further enhanced by a compatible tie coat, using a compatible chemistry which bonds to polar PET film with apolar Liquid Crystal polymer to create a strong and uniform colour shift film for further use in security threads and bank notes .

Yet another objective of the present invention there is to provide an improved security film that is far more stable and does not change its characteristics during the manufacturing process.

Yet another objective of the present invention there is to provide an improved security film that is far more stable and does not change its colour shift properties during the paper making process and retains it’s characteristics for a longer period of time during circulation.

Yet another objective of the present invention is to provide an improved security film that once bonded or laminated to a metalized, de-metalized, black ink printed/coated substrate, will give the wide spectrum colour shift effect, in a pre designed spectrum, consistently and till the end of effective life of the currency note.

Yet another object of the present invention is to provide an improved security film using Tie coat process which enables the security thread manufacturer to use the step of lamination of liquid crystal film based carrier film to receptor film which may be mettallised/demettalised and/or dark/opaque coated/printed substrate, without the process of detaching the LC film carrier . The tie coated carrier film, creates a robust structure and protects the fragile LC Polymers from detaching during the process of security thread manufacturing, insertion into security paper or during currency in circulation. Yet another objective of the present invention is to provide an improved security film that helps to maintain the desired properties of Liquid crystal film, in a pre defined spectrum values, consistently and till the end of effective life of the currency note , by avoiding an over lamination film using using a robust laquer, as a protective layer .

Yet another objectve of the present invention is to provide a method of manufacturing an improved security film that discloses a more complex and wide spectrum colour shift film using a novel method of manufacturing liquid crystal film.

SUMMARY OF THE INVENTION

The present invention discloses a high security wide spectrum colour shift film and a method of manufacturing a high security film with wide spectrum colour shift effect that is far more stable and does not change its characteristics during the manufacturing process.

The present invention provides an improved security film using Tie coat process which enables the step of lamination of liquid crystal to receptor mettalised/de- mettalised and/or dark/opaque coated/printed substrate, without the process of detaching the Liquid Crystal film carrier.

The present invention discloses an improved high security colour shift film with added features, having a robust tie coat that is more economical than a film laminate, it provides protection against sebum and dirt. The improved high security colour shift film has longer shelf life in long term external use and also withstand several mechanical stress and strain, thereby compensates for the brittle/cracking nature of liquid crystal film.

According to one embodiment of the present invention, discloses construction of high security colour shift film as described by the present invention. The object of the present invention is to introduces a new, improved, eco-friendly, high secure and complex film, which is nearly transparent, clear to look at, and optionally, will display a pre-defined set of spectral values when tilted at specific angles.

According to another embodiment of the present invention, discloses method of manufacturing high security film, which once formed may be incorporated in valuable documents such as bank notes to provide an improved high security colour shift film as disclosed in the present invention.

According to another embodiment of the present application discloses a Highly secure and complex Colour shift film comprising of at least two different liquid crystal layer wherein the colour shift film exhibits colour shift effect over a wider spectrum/wavelength and wherein, at least one of the Liquid crystal film is adhered/ bonded to a metalized, de-metalized, black ink printed/coated polar substrate through a tie coat layer and the two Liquid crystals are bonded through an adhesive layer.

BRIEF DESCRIPTION OF THE INVENTION

The nature and scope of the present invention will be better understood from the accompanying drawings, which are by way of illustration of a preferred embodiment and not by way of any sort of limitation. In the accompanying drawings,

Fig. 1 illustrates a basic construction of liquid crystal‘A’ film defined as LC Film Roll 1 in the present invention.

Fig. 2 illustrates a basic construction of liquid crystal Έ’ film defined as LC FilmRoll 2 in the present invention.

Fig. 3 illustrates another embodiment of high security wide spectrum colour shift film formed by combining roll 1 and roll 2 herein defined as wide spectrum tie adhered LC Film Roll 3 in the present invention. Fig. 4a illustrates high security wide spectrum colour shift film anddetaching the liner in the present invention. This process may be done during or before production of security thread operation,

Fig. 4b illustrates another embodiment of construction of high security wide spectrum colour shift film adhering through tie coat on PET substrate in the present invention. This process may be done during or before production of security thread operation,

Fig. 5a illustrates a basic construction of robust security thread with a cast & cure top lacquer as disclosed in the present invention. This process may be done during production of security thread operation.

Fig. 5b illustrates a basic construction of robust security thread using the tie coat process as disclosed in the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides an improved high security colour shift film with a robust top coating, which is more economical than a film laminate, has higher/controlled gloss versus reflected light as also provides protection against sebum and dirt, to ensure longer life to the security features even in long term external use and against severe mechanical stress and strain. The high security colour shift film of the present invention, compensates for the brittle nature of LCs (Liquid Crystals) and also provides better protection against many daily chemicals, such as those found in cleaning and washing. The high security colour shift film of the present invention is the most secure and durable security thread for insertion in bank note paper, including insertion in highly alkaline pulp slurry, under wet conditions.

The present specification is further described with reference to terminology used in relation to the present invention have been defined herein below: LC: Means liquid crystal polymers, that can be chiral, nematic/cholesteric or combination thereof and has a specific wavelength;

LC Film: means LC film formed after casting/coating/printing and subsequently drying and curing. LC film is formed on a support film, which is typically a clear, dimensionally stable PET film;

Carrier Film: means a film, like but not limited to, PET film, PP film, PC film and like;

PET: Film made from Polyethylene terephthalate resin BOPET film ranging from 3 microns to 36 microns, preferably 6 microns to 24 microns, more preferably from 9 microns to 12 microns

Tie Coat: Tie coat, also known as anchor coat, is coated onto a film (in this case PET film), for better adhesion of apolar resins/inks/coatings/polymer (LC) to form a bond between polar PET to apolar polymeric resin, eg. LC polymer, for the purpose of this invention. Tie coat also ensures that the bond between PET film and LC becomes one unified bond upon curing the whole construction;

Opaque Printing: is defined to cover, any kind of metallic, non-metallic, carbon ink based, titanium oxide based inks etc. The opacity and dark properties of printing ink is of relevance, while the minerals or metals or other inorganic materials used to make ink, is not a limiting factor. Preferably, dark black background is found to be showing the best colour shift properties;

Tie II Coat: for this invention, means flash cured tie coatis defined as an adhesive between layers of LCs or layers of PET films and LC or layers of LC Or coated films or any kind of coatings. This tie coat may have characteristics like that of PSA (pressure sensitive adhesives) or non PSA and may be a formulation of resins, one or more like, Polyvinyl alcohol, polymides derivatives or other polymers, which include acrylics, nylons, UV curable Acrylates, polyurethanes or combination thereof. The curing process may be done by using hot air or LED or UV. The solvents may be water, toluene’s, xylenes, Kenotic or family of Cyclohexanone. The combination and list of polymers, resins and organic materials and solvents are not limited.

Receptor Film: means the “receiving” film. For the purpose of this invention it relates to the black/dark printed/coated or metal printed or a de- mettalised film or indicia/text/graphic enhanced film, upon which the “donor” LC film is bonded to create the colour shift effects, at discreet areas;

Donor Film: a clear, dimensionally stable carrier film, like but not limited to PET film, without a tie coat, which is“transfers” the LC film onto the “receiving” film, on the desired side of the“Receptor film” ;

Tie Coated Film: a clear, dimensionally stable carrier film, like but not limited to PET film, with a specific tie coat, for effectively bonding between LC polymers, during the LC coating/printing process, ensuring effective wetting, prior to UV/LED curing, as well as effective bonding to “Receptor” film, during the Security Thread making process;

Tie Coated LC Film: a clear, dimensionally stable carrier film, like but not limited to PET film, coated with a bond enhancing tie coat for boding a PET film having higher dyne values (range of 40-65), to an apolar LC polymer, during the LC coating/printing process, ensuring effective wetting, prior to UV/LED curing, as well as effective bonding to“Receptor” film, during the Security Thread making process;

Spectral Values: are defined as values as measured using a spectrophotometer, like Carl Zeiss (as mentioned in the patent), and recording peaks and valleys of the wavelengths. The range of the visible values are as shown in Figure A. These values are given in nanometers (nm) and these nm values correspond to the colour spectrum of VIBGYOR.; NIR: means Near Invisible Red. This is the other end of the spectrum, which is not readily visible to eye, when light is reflected on it, like 750 nm and beyond;

NIV: means Near Invisible Ultra Violet spectrum of the colour range, like 380 nm and under. Liquid Crystal Film, is a key film responsible for discreet colour shift values, is essentially clear at first instance, with a mild hue of colours, created by reflection of random light, at random angles, but when laminated to a Metalized, or de- metalized and/or opaque coated and/or opaque ink printed receptor film, forms a colour shift effect of pre-defined colour values, also known as“spectral values” and once slit into micro tapes, ends up as a high security thread. Using a tie coated LC Film, as disclosed in the invention provides protection against sebum and dirt. The improved security thread has longer shelf life in long term external use and also withstand several mechanical stress and strain. Optionally other security elements, like but not limited to magnetic elements, machine readable, light source readable, UV fluorescent pigments, magnetic print block, DNA taggent etc. UV fluorescent pigments, etc may be added. After, insertion into paper, during the process of making bank note paper, it’s final end use is to secure currency/banknotes of various countries.

The present invention provides an improved, purpose engineered, eco-friendly and high secure and complex colour shift security film, which is nearly transparent, clear to look at, and optionally, after affixing to a darker background, when tilted it will display a pre-defined set of spectral values when tilted as specified angles. This Visible spectrum is defined in nanometers as values. The spectral values (as shown in figure‘A’) will define the visible colour to our eyes, and will change from gracing angle to tilted angle. Following visible spectrum (380nm to 750nm) will shed more light on the VIBGYOR in nanometers, which in turn will define the colour range of the spectrum.

Fig. A This complex LC Coated film is nearly clear to look at the first instance, but once it is bonded to an opaque substrate, like but not limited to a black printed/coated film, will show a pre specified colour shift effect, at specific angles, at the points where the opaque design or indicia are located.

The present invention provides an improved security film using Tie coat process which enables the step of lamination of liquid crystal film to receptor mettallised/demettalised and/or dark/opaque coated/printed substrate, without the process of detaching the LC film carrier

End use of this security film will be to attain a particular set of colour shift within the reflected light phenomena, like but not limited to blue changing to green ( 470nm to 540 nm) on angle of light* or a wider range like Blue changing to Red (450nm to 700nm), which is a more wider colour change, in the spectrum of VIBGYOR Light. This security film once bonded or laminated to a metalized, de- metalized, black ink printed/coated, Receptor substrate, will give the wider range of colour shift effect.

*The angle of viewing, in relation to colour shift, is typically 35 degrees to 45 Degrees, from gracing view (plain layflat view Fig B).

Fig. B

Needless to say that that the wider the spectrum of colour-shift, more difficult it is to replicate and control. Also, it is important to know that the adhesion value of the two substrates will ensure that the end product will comply to the endurance specifications as needed by various customers, depending upon the expected life of the properties of colour shift properties and the end use of the product. There can be multiple combination for complex colour shift security film with desired wider colour shifts which form a part of the present invention. Below are the non-limiting examples of colour shift security film with wider colour shifts:

Example 1:

Step 1: LC coated on PET - Colour shift BLUE (450nm) to UV

Step 2: LC coated on PET - NIR to Red (700 nm)

Step 3: Lamination of LC Lilms - Colour shift Blue to Red (450nm to 700nm)

Preparation of high security film for Example 1:

We took a clear PET film, preferably with high gloss, thermally stable properties, gravure coated a proprietary formulation of liquid crystals, known to create a particular colour spectral value, in this case 450 nm to invisible range of UV, dried the solvents off the coating, cured the coating, using UV Curing method, and optionally pasing through chilling rollers, we wound the web on a shaft. - Roll 1.

We took another clear PET film, preferably with highgloss, thermally stable properties, gravure coated a proprietary formulation of liquid crystals, known to create a particular colour spectral value, in this case visible Red 700 nm (+/-15 nm) to NIR (near invisible infrared) range, dried the solvents off the coating, cured the coating, using UV Curing method, and optionally passing through chilling rollers, we wound the web on a shaft. - Roll 2.

We laminated Roll 1 to Roll 2, using a very clear adhesive, compatible to both LC films, and flash cured, the structure, using UV light source 120 -300 w/cm2, as mentioned in the patent. The curing of LC polymers can also be cured by using LED light source (365nm), and the curing system should not be considered as a limitation.

To get the values of this laminated film, we recorded the following results, using a Zeiss MCS 500 series. Result of the Experiment, as seen under a Spectrophotometer*

Reflection spectra of liquid crystal Blue to Red colour shift film

The described spectroscopic measuring mode under different angles characterizes in a realistic and comprehensive way the angle dependent colour shift of liquid crystal films

Example 2:

Step 1: LC coated on PET - Colour shift Turquoise (490nm) to UV

Step 2: LC coated on PET - NIR to Red(700nm)

Step 3: Lamination of LC - Colour shift Turquoise to Red (490nm to 700nm)

Preparation of high security film for Example 2:

We took a clear PET film, preferably with high gloss, thermally stable properties, gravure coated a proprietary formulation of liquid crystals, known to create a particular colour spectral value, in this case 490 nm to invisible range of UV, dried the solvents off the coating, cured the coating, using UV Curing method, and optionally passing through chilling rollers, we wound the web on a shaft. - Roll 1.

We took another clear PET film, preferably with high gloss, thermally stable properties, gravure coated a proprietary formulation of liquid crystals, known to create a particular colour spectral value, in this case visible Red 700 nm (+/-15 nm) to NIR (near invisible infrared) range , dried the solvents off the coating, cured the coating, using UV Curing method, and optionally passing through chilling rollers, we wound the web on a shaft. - Roll 2..

We laminated Roll 1 to Roll 2, using a very clear adhesive, compatible to both LCs, and flash cured, the structure, using UV lightsource(120 -300 w/cm2), as mentioned in the patent. The curing of LC polymers can also be cured by using LED light source (365nm), and the curing system should not be considered as a limitation.

To get the values of this laminated film, we recorded the following results, using a Zeiss MCS 500 series.

Result of the Experiment, as seen under a Spectrophotometer*

Reflection spectra of liquid crystal Turquoise to Red colour shift

This invention will find its end use in production of security tapes/thread, which is presently used in Bank Notes/currency notes.

Precise Coating of liquid crystals, gives a wider spectrum of colourshift values, consistent colour shift values in linear terms as well as cross directional terms and is considered more secure.

According to one embodiment, the present application discloses ahigh secure and complex colour shift film comprising of at least two different liquid crystal layer wherein the colour shift film exhibits colour shift effect over a wider spectrum/wavelength and wherein, at least one of the Liquid crystal layer is adhered/ bonded to apurpose engineered“receptor filrri’using a tie/adhesive coat layer and further the two Liquid crystals are bonded through yet another tie coat layer. Both tie coats are purpose engineered to adhere apolar LC films to themselves as well as to adhere to polar films, like PET film, after drying and/or curing.

According to another embodiment, the present application discloses ahighly secure and complex Colour shift film wherein, the obverse face of the Liquid crystal layer is further coated with a heat seal top coat layer during the process of manufacture of security thread, so as to enable the thread to adhere to paper fibers.

According to another embodiment, the present application discloses ahighly secure and complex Colour shift film wherein, the obverse face of the substrate is optionally coated with a fluorescent coat prior to coating of heat seal top coat layer, during the process of manufacture of security thread. According to one embodiment of the present application, in the high security colour shift film of the present invention a tie coat based LC film is laminated onto/bonded to the“receptor” substrate, display the desired colour shift spectral values as also display higher/controlled gloss versus reflected light. A tie-coat is a layer of coating that acts as a bridge between a PET and the liquid crystal coating layer. The tie-coat provides a transitional layer that bonds or improves the adhesion of the two separate coatings.

According to another embodiment of the present application, in the high security colour shift film of the present invention, is also protected by a robust overcoat like by not limited to a clear, high UV curable lacquer which helps to protect the robustness of the colour shift qualities. This process includes a lacquer coating, having high gloss, scratch resistant, sebum resistant, dirt resistant and UV protective property. This coating may be engineered as per the specification of the end user, and is by no way to be a limitation this process is ideally done during the process of manufacture of security thread if the robustness is not fortified by a tie coated PET film. Optionally, the tie coated complex LC film, as described in this invention can also be further fortified by using a lacquer coating on face side, i.e. on PET face side, in this case.

According to one embodiment, the colour shift film of the present application which displays consistent spectral values throughout the circulation life of the bank note, and laminating this robust colour shift security film with wide spectrum complex spectral values onto the main“receiver” substrate, to display the desired colour shift spectral values, can subsequently be used to produce high security threads for insertion in bank note paper.

According to another embodiment of the present application, the high security colour shift film of the present invention is prepared in such a manner so as to exhibit a wide spectrum colour shifting film, like but not limited to a spectrum of 450/700 nm or 490/700 nm, which is technically complex, wider spectrum, compared to currently available colour shift film with narrow spectrum like Blue to Green 470/540 nm. The wide spectrum values given are only for examples and by now way a limitation to this invention.

According to another embodiment of the present application, the high security colour shift film of the present invention exhibits varied colour combinations from the VIBGYOR spectrum thereby making it possible to design more secure colour- shift combinations. It is difficult to exhibit/simulate such wide spectrum using vacuum metallizing or sputtering technology, as there are inherent limitations in layers one can apply with different metals or the inorganic materials, to get different types of colour shades.

According to another embodiment of the present application, the high security colour shift film of the present invention helps in doing commercially feasible research to find more secure combinations. With the new coating process, smaller, consistent and computer-controlled production is commercially possible. Example, with the present invention, a short run as small as 10 meters can be done successfully and repeatedly, when compared to at least 5000 meters of a non- consistent run in a vacuum chamber. This process allows different combinations of colour shift and makes it more commercially feasible.

According to another embodiment of the present application the substrate is selected fromlike but not limited to, PET film .

According to another embodiment of the present application the heat seal top coat layer comprises of anti-sebum and anti-dirt coating and consists of material such as like but not limited to, UV curable lacquer coatings.

According to another embodiment of the present application the Liquid crystalLiquid crystals can be chiral, nematic/cholesteric dopants or combination thereof and forms a specific wavelength and colour shift properties. The ratios of such crystals, solid contents and dilution in particular solvents will result in specific wavelengths of colour shift values.

According to another embodiment of the present application the adhesive layer is selected/made of like but not limited to, acrylics, nylons, UV curable Acrylates, polyurethanes etc. as defined in the patent disclosure and is purpose engineered towards the desired property

According to another embodiment of the present application the tie coat layer is selected/made of like but not limited to, UV curable Acrylates, polyurethanes etc..as defined in the patent disclosure and is purpose engineered towards the desired property

The present invention discloses various method of manufacturing an improved high security colour shift film, said method of manufacturing colour shift film may be brought out either individually or in combination, so as to manufacture the high security thread as disclosed in the present invention.

According to one embodiment, the method of manufacturing Highly secure and complex Colour shift film comprises the steps of:

a. Coating Liquid crystal polymer on a dimensionally stable substrate, preferably PET substrate, to form a LC filmof a discreet nano meter wavelength

b. Coating of another Liquid crystal polymer, optionally on a tie coated dimensionally stablesubstrate preferably PET substrate to form another LC film of a wider range of nano meters wavelength ;

c. Bringing together the stack of LC films and PET films obtained in step (a) and (b) on the side of the Liquid crystal film, and curing the same using an flash cured tie coat layer without any application of hot air; d. Delaminating/peeling off the substrate from one side of the film to obtain a high security film for further process of manufacture of security thread.

According to one embodiment of the present invention Fig.1 -Fig 4a and 4b illustrates a complex wide spectrum liquid crystal film, which once formed may be incorporated to provide a robust improved high security colour shift film as disclosed in the present invention.

Fig. 1 illustrates a liquid crystal film on a PET(l) carrier, Said PET(l) is coated with a LC polymers to form a Liquid crystal film(2) of consistent colour shift properties in a pre-defined discreet range. The Liquid crystals polymeric formulationisa mixture of chiral, nematic/cholesteric, certain dopants, surfactants in precise ratios known to display a specific wavelength that is different from the liquid crystal polymeric formulation used in LC Film (3) as shown in figure Fig. 2.

Fig. 2 illustrates a liquid crystal film, wherein the PET (1) is used as a carrier substrate. Said PET(l) is coated with a tie coat, which forms a clear dimensionally stable film, after drying and curing, which is engineered to enable better coat and adhere to apolar polymers like LC polymers and after drying and curing, to form a Liquid crystal film(3) of consistent colour shift properties in a pre-defined discreet range. The Liquid crystals polymeric formulationisa mixture of chiral, nematic/cholesteric, certain dopants, surfactants in precise ratios known to display a specific wavelength that is different from the liquid crystal polymeric formulation used in LC Film (2) as shown in figure Fig. 1.

Fig. 3 illustrates a High security liquid crystal film, wherein both the Liquid Crystals film as disclosed in Fig. 2 and Fig. 3, are brought together, using a compatible adhesive as mentioned in the patent, to make High Security Liquid Crystal film, such that the film has wider range of colour shift. Fig.4a illustrates a High security liquid crystal film, that has wider range of colour shift spectrum values and wherein the PET substrate (1) from one or both sides of the high security film shown in figure (3) can delaminated/peeled/removed off.

Fig.4b illustrates a High security liquid crystal film, that has wider range of colour shift and wherein the high security liquid crystal film is adheredto the PET substrate (1) via tie coat (9).

The present invention discloses several methods of manufacturing an improved high security colour shift film, which are described as follows

Step 1: Coating of the one Liquid Crystal(2) on substrate PET -> Drying of Solvents -> UV curing -> Roll 1

Step 2: Coating of second Liquid Crystal(3) on substrate PET -^Drying of Solvents ->UV curing -> Roll 2

Step 3: Combine the Roll 1 and Roll 2 on Liquid crystal side with the use of suitable Flash cured tie coat(5) to obtain security film with wide spectrum -> Roll 3

Step 4: On detaching one or both layers of PET substrate(l) from Roll 3, roll 4 is now ready for further use in robust High security thread

Liquid crystals formed from mixture of LCs as defined, and these may include polymershaving specific characteristically effects, such as chiral, nematic/cholesteric; and certain dopants, or combination thereof, are dissolved/mixed in certain ratios and stirred in solvents are used as coating to achieve a desired colour shift effect over the PET. According to another embodiment of the present inventionFigure 5, which depicts essentially a construction of high security thread, with wider spectrum of colour shifting characteristics, also discloses two inventive steps:

In figure 5(a), the process of a cast cure lacquer as shown at part (6), on the face side of the colour shift thread, forms a part of the construction, which gives higher robustness and ability to the thread to maintain its consistent colour shift properties and characteristics during insertion of thread into paper, going through the stress of printing, including intaglio printing and while the currency is in circulation.

In Figure 5(b), the process of addition of Tie Coated film (part (9) as tie coat and part 1, as a PET film), laminated to the rest of the construction, gives higher robustness and ability to the thread to maintain its consistent colour shift properties and characteristics during insertion of thread into paper, going through the stress of printing, including intaglio printing and while the currency is in circulation.

The process of bonding the two apolar LC Films, using a flash cured tie coating, gives higher robustness and ability to the thread construction as a whole, to maintain its consistent colour shift properties and characteristics during insertion of thread into paper, going through the stress of printing, including intaglio printing and while the currency is in circulation.

Figure 5(a) describes various layers of functional coatings as seen in a Security thread.

Receiver substrate (1) as defined as receptor and known to security thread manufacturers may be metallized /De-metallized having indicia(referred as (4) in the fig, may be in form of text, numbers, graphics etc.. The said receptor substrate is adhered /laminated with High security Liquid crystal film (as described in fig. 4a), to the said receptor substrate using aTie II (as defined ) coat, which is referred as (5) in said figure on the face side to form a high security web/roll , which is further coated with cast and cure lacquer (6), and subsequently coated with heat seal top coat (7). Receiver substrate (1) is optionally coated with fluorescent coat (8) on the obverse side of the substrate followed by heat seal top coat (7) on top of the fluorescent layer (8).

This construction of security thread web of roll is then slit into tapes/thread, for further insertion into Bank Note Paper.

Outline of process of Manufacturing the High Security Film based robust security thread as per fig 5a is described hereinafter in detail: a. Receiver substrate as shown as substrate (1) in fig 5a;

b. Coating of“Tie coat II” as defined referred as (5) on substrate (1);

c. Drying/ UV curing of coated substrate the web received from (b);

d. Lamination of Robust high security liquid crystal film (donor film as mentioned in fig 4a) from the face side of the high security thread substrate as shown in fig 5a;

e. Coating of cast and cure solution(6);

f. UV curing/drying and optionally chilling of web as obtained from step e; g. Coating heat seal lacquer on Face side (7);

h. Receiver substrate (1) is optionally coated with fluorescent coat (8) on the obverse side of the substrate (1);

i. Coating heat seal top coat (7) on top of the fluorescent layer (8) on the web received from step (h);

j. Winding the web on a shaft, for further slitting into security threads/tapes

Figure 5(b) describes various layers of functional coatings as seen in a Security thread.

Receiver substrate (1) as defined as receptor and known to security thread manufacturers may be metallized /De-metallized having indicia(referred as (4) in the fig, may be in form of text, numbers, graphics etc.. The said receptor substrate is adhered /laminated with High security Liquid crystal film (donor film as mentioned in fig 4b, such donor film is a tie coated PET film as a substrate (1) in fig. 5b), to the said receptor substrate using aTie II (as defined ) coat, which is referred as (5) in said figure on the face side to form a high security web/roll, (That may be optionally coated with cast and cure lacquer (6)) and subsequently coated with heat seal top coat (7). Receiver substrate (1) is optionally coated with fluorescent coat (8) on the obverse side of the substrate followed by heat seal top coat (7) on top of the fluorescent layer (8).

Outline of process of Manufacturing the High Security Film based robust security thread as per fig 5b is described hereinafter in detail: k. Receiver substrate as shown as substrate (1) in fig 5b;

l. Coating of“Tie coat II” as defined referred as (5) on substrate (1);

m. Drying/ UV curing of coated substrate the web received from step (k); n. Lamination of Robust high security liquid crystal film ( donor film as mentioned in fig 4b, such donor film is a tie coated PET film as a substrate (1) in fig. 5b) to the face side of the“receptor” high thread substrate (1) as shown in fig 5b;

o. Coating heat seal lacquer on face side (7);

p. Receiver substrate (1) is optionally coated with fluorescent coat (8) on the obverse side of the substrate (1);

q. Coating heat seal top coat (7) on top of the fluorescent layer (8)on the web received from step (p);

r. Winding the web on a shaft, for further slitting into security threads/tapes

The problem faced by known processes of LC films or PVD (particle vapour deposition of inorganic stacks)needs bigger runs, thus wasting several square meters of PET film which is/wasis not commercially feasible and needed more research to find wide range secure combinations, but now it is possible as per the present invention. With the new coating and laminating processes as disclosed in the present invention, smaller, consistent and computer controlled production is commercially possible. For example, with the process as disclosed in the present invention, a short run as small as 10 meters can be done successfully and repeatedly to get various complex colour shift effects, when compared to at least 5000 meters of a non consistent run in a vacuum chamber. Our disclosed process allows different combinations of colour shift and is more commercially feasible.

Further advantages provided by the improved high security colour shift film involves:

Economical to the consumers and hence can meet consumers need;

Cost benefit to manufacturer, since the improved high security colour shift film has less layers of films and coatings, makes this product and whole system as a most economical and friendly to use.

Simpler and easy production method, as liquid crystal curing entails heat drying and UV curing, the system of coating & cast curing is a much simpler system for production processes, compared to additional laminating of film layers. Famination entails heat and pressure, which affects the liquid crystal property, as liquid crystals are sensitive to heat and pressure, while liquid crystal has affinity towards heat and UV curing.

In conclusion, the present invention provides an improved high security colour shift film with added complex security features, having a robust top coat that is having wide spectrum of colourshift effects than the present methods. The said robust complex security film can be used to produce complex high security thread, having a robust structures as disclosed, and will be more economical compared to transfer method of LC film or Vacuum deposited particle based colour shifting film or security thread made therefrom. The end product produced as per our invention shows higher or controlled gloss versus reflected light as well asprovides protection against sebum and dirt. The improved high security colour shift film has longer shelf life in long term external use and may also withstand several mechanical stress and strain, which is otherwise inherent weak link while using liquid crystal or inorganic ultra thin depositions, within the structure of a security thread. These improved high security colour shift film, can be used to make security thread, as shown in above processes. The structure of the security thread can be enhanced further byoptionally printing/coating other security elements, like but not limited to magnetic elements, machine readable, light source readable, UV fluorescent pigments, magnetic print block, DNA taggent etc. After, insertion into paper, the security thread is usually displayed like“windows” during the insertion process in mould made bank note paper. It is also known as Currency paper, and after security printing, it is known as currency notes, and is used in countries worldwide.

The present invention has been described with reference to some drawings and a preferred embodiment purely for the sake of understanding and not by way of any limitation and the present invention includes all legitimate developments within the scope of what has been described herein.

Claims

I claim:

1. A robust, high secure, complex colour shift film comprising at least two liquid crystal polymeric layersindividually coated to acarrier film,

wherein the said Liquid crystal polymeric layers are subsequently bonded through an adhesive/tie layer to each other,

Wherein the carrier film is optionally tie coated,

wherein the said colour shift film exhibits colour shift effect over a wider spectrum/wavelength, covering NIV to NIR colour spectrum.

2. A robust, high secure, complex colour shift film comprising at least two liquid crystal polymeric layers individually coated to a carrier film,

Wherein the carrier film is optionally tie coated,

whereinthe carrier film is delaminated / peeled off from one side of the said liquid crystal layer,

whereinthe said colour shift film exhibits colour shift effect over a wider spectrum/wavelength, covering NIV to NIR colour spectrum.

3. A robust, high secure, complex colour shift film as claimed in claim 1 or claim 2wherein the carrier film is selected from Polyethylene terephthalate (PET), or PP (polypropelene) film, PC (Polycarbonate) Film and the like.

4. A robust, high secure, complex colour shift film as claimed in claim lor claim 2wherein the Liquid crystal film is chiral, nematic/cholesteric or combinationsthereof , which diplays colour shift spectral values of specific wavelength.

5. A robust, high secure, complex colour shift film as claimed in claim 1 or claim 2 wherein the Adhesive/ layer is selected from a formulation of resins, one or more like Polyvinyl alcohol, polymides derivatives or other polymers, which include acrylics, nylons, UV curable Acrylates, polyurethanes or combination thereof.

6. A robust, high secure, complex colour shift filmas claimed in claim 1 or claim 2 wherein the tie coat layer is selected from UV curable Acrylates, polyurethanes or the like.

7. A robust, high secure, complex colour shift filmas claimed in claim 1 or claim 2displaying colour shift values of NIV to NIR range, of the spectral values of the VIBGYOR spectrum i.e from Blue spectrum to Red spectrum.

8. A robust, high secure, complex colour shift filmas claimed in claim 1 or claim 2 displaying wider range of values in nano meters, when seen at different angles, preferably in the range between 450 nm to 700 nmwith a variation of 15nm on both ends.

9. A high security thread comprising the robust, high secure, complex colour shift film claimed in claim lor claim 2 wherein the carrier film is metallized /De metallized having indicia in form of text, numbers, graphics and the like.

10. The high security thread as claimed in claim 9 wherein, the face side, which displays the colour shift properties is optionally coated with cast and cure lacquer.

11. The high security thread as claimed in claim 10 wherein, the said security thread is further coated with a heat seal top coat layer.

12. The high security thread as claimed in claim 9 wherein, the obverse face of the substrate is optionally coated with a fluorescent coat.

13. The high security thread as claimed in claim 9 or claim 12 is coated with a custom designed and purpose built heat seal lacquer.

14. The high security thread as claimed in cliams 9,10,11, 12, 13which further incorporates various machine readable and light source readable security elements, like magnetic inks, magnetic print blocks, DNA taggants, security taggants etc.

15. A method of manufacturing a wide spectrum color shift film comprising the steps of laminating the robust high security liquid crystal film to a metallised/demetallised and/or dark/opaque coated/printed and tie coated with receiver/receptor substrate, thereby eliminating the step of detaching the LC film carrier.

16. A method of manufacturing Highly secure and complex Colour shift film comprising the steps of:

a. Coating Liquid crystal polymer on a dimensionally stable substrate, preferably PET substrate, to form a LC film of a discreet nano meter wavelength;

b. Coating of another Liquid crystal polymer optionally on a tie coateddimensionally stable substrate preferably PET substrate to form another LC film of a wider range of nanometers wavelength;

c. Bringing together the stack of LC films face to face and PET films obtained in step (a) and (b) on the side of the Liquid crystal filmsand curing the wet tie/adhesive coatby using UV flash curing equipment without use of hot air,

d. Winding the web onto a shaft.

17. A method of manufacturing Highly secure and complex Colour shift film comprising the steps of:

b. Coating of another Liquid crystal polymer optionally on a tie coateddimensionallystable substrate preferably PET substrate to form another LC film of a wider range of nanometers wavelength; c. Bringing together the stack of LC films face to face and PET films obtained in step (a) and (b) on the side of the Liquid crystal films and curing the wet tie/adhesive coat by using UV flash curing equipment without use of hot air,

d. Delaminating/peeling off the substrate from one side of the film to obtain a high security film for further process of manufacture of security thread.

18. The method of manufacturing a wide spectrum color shift film as claimed in claim 16 or claim 17, wherein step (a) forms Roll 1.

19. The method of manufacturing a wide spectrum color shift film as claimed in claim 18, wherein Roll 1 comprises of;

a. Coating liquid crystal polymer on a dimensionally stable substrate, preferably PET (1) to form a LC film (2) in a pre -defined discreet range;

b. Drying of solvent of the coating;

c. Curing the coating using UV curing method;

d. Optionally passing through chilling roller; and

e. Winding the web (Roll 1) on a shaft.

20. A method of manufacturing a wide spectrum color shift film as claimed in any one of the claims 16 or 17, wherein step (b) forms Roll 2.

21. A method of manufacturing a wide spectrum color shift film as claimed in claim 20, wherein Roll 2 comprises of;

a. Coating liquid crystal polymer on a dimensionally stable substrate, preferably PET (1) to form a LC film (3) of consistent colour shift properties in a pre defined discreet range.

b. Drying of solvent of the coating;

c. Curing the coating using UV curing method;

d. Optionally passing through chilling roller; and

e. Wounding the web (Roll 2) on a shaft.

22. A method of manufacturing a wide spectrum color shift film as claimed in claim 16 or 17, wherein step (c) forms Roll 3.

23. A method of manufacturing a wide spectrum color shift film as claimed in claim 22, wherein Roll 3 comprises: a. Combining the stack of LC films (2,3)and PET films obtained as roll 1 and roll 2 on the side of the Liquid crystal film using a very clear tie coat II (5), compatible to both LC films;

b. Curing the same using a flash cure tie coat II layer without any application of hot air to form Roll 3, such that the film has wider range of colour shift.

24. A method of manufacturing a wide spectrum color shift film as claimed in claim 17, wherein Roll 4 is formed by delaminating/peeling off the PET substrate from one or both sides of the film to obtain a high security film for further process of manufacture of security thread.

25. A method of manufacturing a wide spectrum color shift film as claimed in any one of the claims 16 to 24, wherein liquid crystals polymer selected are dissolved/mixed in precise ratios with solvent to form a coating layer of LC.

26. A method of manufacturing Highly secure and complex Colour shift film comprising the steps of:

b. Coating of another Liquid crystal polymer on a tie coated dimensionally stable substrate preferably PET substrate to form another LC film of a wider range of nanometers wavelength;

c. Bringing together the stack of LC films and PET films obtained in step (a) and (b) on the side of the Liquid crystal film and curing the same using a flash cured tie coat layer without any application of hot air;

d. Laminating the structure/donor onto the receptor film to obtain a high security film for further process of manufacture of security thread.

27. A robust high security thread made of various layers of functional coating comprising:

a. Receiver substrate (1) defined as metallized /De-metallized receptor having indicia (4) on the face side;

b. Coating of the wide spectrum color shift film obtained in claims 1 to 26 over the Receiver substrate (1) using a tie coat II (5) on the face side; c. Further coating of Cast and cure lacquer (6) over the wide spectrum color shift film obtained in claims 1 to 23 and subsequently coating with heat seal top coat (7);

d. Optionally fluorescent coating (8) on the Receiver substrate (1) on the obverse side of the substrate followed by heat seal top coat (7) on top of the fluorescent layer (8), finally to form a high security web/roll;and

e. high security web/roll formed in step (d) is further slit into tape/thread for further insertion into bank note paper.

28. A method of manufacturing the robust security thread as claimed in Claim 27, comprising the steps of:

a. Receiver substrate as shown as substrate (1) ;

b. Coating of“Tie coat II” as defined referred as (5) on substrate (1);

c. Drying/ UV curing of coated substrate the web received from (b);

d. Lamination of Robust high security liquid crystal film (donor film ) from the face side of the high security thread substrate;

e. Coating of cast and cure solution(6);

f. UV curing/drying and optionally chilling of web as obtained from step e;

g. Coating heat seal lacquer on Face side (7);

i. Coating heat seal top coat (7) on top of the fluorescent layer (8);

29. A robust high security thread made of various layers of functional coating comprising:

f. Receiver substrate (1) defined as metallized /De-metallized receptor having indicia (4) on the face side;

g. Laminating the high security liquid crystal film (donor film) obtained in claims 1 to 26 over the Receiver substrate (1) using a tie coat II (5) on the face side;

h. Such donor film is a Tie coated PET film as a substrate as obtained in claims 1 to 26.

i. Optionally fluorescent coating (8) on the Receiver substrate (1) on the obverse side of the substrate followed by heat seal top coat (7) on top of the fluorescent layer (8), finally to form a high security web/roll;and

j. high security web/roll formed in step (i) is further slit into tape/thread for further insertion into bank note paper.

30. A method of manufacturing the robust security thread as claimed in Claim 29, comprising the steps of:

a. Reciver substrate as shown as substrate (1) ;

b. Coating of“Tie coat II” as defined referred as (5) on substrate (1);

c. Drying/ UV curing of coated substrate the web received from step (k); d. Lamination of Robust high security liquid crystal film ( donor film), such donor film is a tie coated PET film as a substrate (1) to the face side of the“ receptor” high thread substrate (1);

e. Coating heat seal lacquer on face side (7);

f. Receiver substrate (1) is optionally coated with fluorescent coat (8) on the obverse side of the substrate (1);

g. Coating heat seal top coat (7) on top of the fluorescent layer (8).