Classifications

• • D—TEXTILES; PAPER
  • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
  • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
  • D01F1/00—General methods for the manufacture of artificial filaments or the like
  • D01F1/02—Addition of substances to the spinning solution or to the melt
  • D01F1/06—Dyes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
  • B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
  • B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
  • B42D25/30—Identification or security features, e.g. for preventing forgery
  • B42D25/355—Security threads
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
  • B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
  • B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
  • B42D25/30—Identification or security features, e.g. for preventing forgery
  • B42D25/36—Identification or security features, e.g. for preventing forgery comprising special materials
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
  • B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
  • B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
  • B42D25/30—Identification or security features, e.g. for preventing forgery
  • B42D25/36—Identification or security features, e.g. for preventing forgery comprising special materials
  • B42D25/378—Special inks
  • B42D25/382—Special inks absorbing or reflecting infrared light
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
  • B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
  • B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
  • B42D25/30—Identification or security features, e.g. for preventing forgery
  • B42D25/36—Identification or security features, e.g. for preventing forgery comprising special materials
  • B42D25/378—Special inks
  • B42D25/387—Special inks absorbing or reflecting ultraviolet light
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K9/00—Tenebrescent materials, i.e. materials for which the range of wavelengths for energy absorption is changed as a result of excitation by some form of energy
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K9/00—Tenebrescent materials, i.e. materials for which the range of wavelengths for energy absorption is changed as a result of excitation by some form of energy
  • C09K9/02—Organic tenebrescent materials
• • D—TEXTILES; PAPER
  • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
  • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
  • D01F1/00—General methods for the manufacture of artificial filaments or the like
  • D01F1/02—Addition of substances to the spinning solution or to the melt
  • D01F1/04—Pigments
• • D—TEXTILES; PAPER
  • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
  • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
  • D01F4/00—Monocomponent artificial filaments or the like of proteins; Manufacture thereof
  • D01F4/02—Monocomponent artificial filaments or the like of proteins; Manufacture thereof from fibroin

Definitions

• the present invention relates to silk fibroin security fibers containing security markers and a process for the preparation thereof.
• a security fiber comprising silk fibroin loaded with inorganic fluorescent chromophore and organic IR absorbing chromophore useful to combat counterfeiting.
• the invention further relates to paper composition containing said loaded silk fibroin fibers.Further the invention provides method for authentication of paper embedded with said security features.
• Security features in banknotes can be classified based on location (embedded in the substrate, loaded in the ink, combined with other security features such as security thread) or based on whether it is visible or not (overt or covert).
• the Indian currency note has microfibers (3 mm in length by tens of microns thick) dispersed in the paper that has bands of UV fluorescent materials that show colors under UV light.
• the Indian currency note has fibers with bands of red or fibers with bands of green or a physical mix of these fibers.
• PCT/EP2010/070172 discloses an encoded object, wherein the object comprising at least one encoded microfiber or nanofiber comprising a polymer and a bleachable fluorophore.
• the polymer may be any of polystyrene, cellulose-acetate-phthalate or poly (lacticco- glycolic acid), polyethylene glycol, ethyl cellulose, polyethylene oxide, wherein fluorophore is coumarin-6 or fluorescein, further the use of an encoded object as described above for preventing counterfeiting of objects, such as food, drugs, etc.
• Silk and other fibers have been commonly used in the manufacture of various banknote papers, intended to provide both additional durability and security. Surface modification and functionalization of silk fibroin fibers/fabric towards high performance textile and biomaterial applications is reported by Guohong Lia et al., in Materials Science and Engineering: C in 32, (4), 2012, pg 627-636.
• 'US7662873' discloses the preparation of fibrous substrates, including textiles, marked with colloidal particle nanobar codes, to the fibrous substrates so prepared, and to methods for detecting the nanobar codes on the fibrous substrates for use in quality control, counterfeiting, and the like.
• the fibrous substrates of said invention are intended to include fibers, fabrics and textiles, and sheet-like structures (Woven, knitted, tufted, stitch-bonded, or non- Woven) comprised of fibers or structural elements, such as natural fibers which include cotton, wool, silk, jute, and linen.
• 'US 307956' disclose manufacturing of paper for bank-notes from palmetto or other long fiber combined with asbestos, wherein the paper for banknotes or other securities containing fibers of colored silk, to indicate the value or origin of the document.
• CN 103103890 discloses a security paper comprises at least two layers of independently molded paper pages, wherein 'fiber textile belt' is arranged between the two paper pages and provided with a security element; the fiber textile belt comprises a silk screen layer woven from a hot melting material with melting point at 50-100°C.
• the Korean publication KR20090063711 discloses a security paper containing silk fiber and a method for discriminating the same, wherein the length of silk fiber ranges from 0.3 to 1.0mm.
• the content of the silk fiber is 5 - 30 weight% based on the whole content of the security paper.
• the authenticity of the said security paper uses microscopic observation.
• microfiber or nanofiber containing polymers preferably hydrophobic polymer, wherein the dye loading into fiber as bulk mixture or extruded fiber into an aqueous pulp solution is difficult.
• Chinese patent CN 102061097 which discloses two-photon fluorescence biological material wherein the two photon fluorescence material is evenly compounded in silk fibre or treated silk fiber.
• the composite material shows excitation in the near infra- red region (780- 1300nm), less than the wavelength of the fluorescence excitation wavelength (600_1300nm).
• the two-photon organic fluorescent material is selected from stilbene derivatives, azo derivatives, thiophene derivatives, fiuorenone derivatives, carbazole derivatives, anthracene derivatives or pyridine derivatives and the like.
• the organic absorber is selected from 2,7-dinitrobenzene vinyl-9,9'-dibutyl fluorene, 2,7-nitrostyryl -9,9 '- two octyl fluorene, 2,7-dibromo-9,9-dibutyl-fluorene alone or in combination thereof.
• the present invention provides an alternate security feature to the existing art. Further, the present invention lay emphasis on loading the microfiber in bulk rather than being limited to surface modifications, which lower the risk of loss of markers when exposed to chemicals or other stimuli, and also making it impossible for the frauders to replicate the technology.
• crystal lattices doped with rare earth ions are known in the art (WO2009/136921). These compounds may absorb radiation at one frequency, and emit radiation at a different frequency, wherein radiation refers to UV, visible, near infrared and infrared radiation. When irradiated with a given wavelength of radiation, these compounds luminesce at a second wavelength and such luminescence may be detected by a detector. Such luminescent compounds are called "luminophores" which may be ions or compounds. Further, IR fluorescent dyes having absorption and emission in near infra-red region (NIK) are used for in vivo imaging due to narrow emission spectra of the dyes and no crossover between fluorophores.
• NIK near infra-red region
• the present invention use this potential feature to develop novel security silk fiber to combat counterfeiting.
• the main objective of the present invention is to provide silk fibroin security fibers containing security markers and a process for the preparation thereof.
• the present invention provides a security fiber comprising silk fibroin loaded with markers selected from inorganic UV fluorescent chromophore and/or organic IR absorbing chromophore that is identified on exposure to said spectral wavelength, wherein said security fiber is useful to combat counterfeiting.
• the UV fluorescent chromophore is selected from inorganic material preferably Sodium yttrium Fluoride-oxide doped with Ytterbium and Thalium.
• the IR absorbing chromophore is selected from organic dye such as Dimethyl ⁇ 4-[l,7,7-tris(4-dimethylaminophenyl)-2,4,6- heptatrienylidene]-2,5-cyclohexadien- 1 -ylidene ⁇ ammonium perchlorate
• the silk fibroin is selected from natural silk fiber or regenerated silk fiber.
• the markers are loaded in the silk fibroin in the ratio ranging between 0.09- 0.1 wt%.
• the fibers are micron size, in the range of 10 microns to 200 microns and thickness of the fibers is in the range of 50 microns to 150 microns.
• a substrate was embedded with security fiber which can be identified on exposure to said spectral wavelength.
• the substrate is selected from textiles, fabrics, plastics, security paper such as bank note paper, passport paper, visa paper, fiduciary paper or labels, packaging materials and the like.
• authentication of substrate embedded with security fiber comprising the loaded markers using UV light or IR light was carried out by irradiating and observing the reflected light from the surface of the substrate.
• the process the preparation of security fiber , wherein said process comprising; i. dissolving lyophilized silk or regenerated silk fibroin in HFIP to obtain a solution in the concentration range of 3 to 12 wt; ii. mixing the markers in to the silk solution of step (1), wherein the concentration of fluorescent marker varies from 0.1 to 10.0 w/v % depending upon the concentration of silk solution; iii. Spinning the mixed solution and extruding the filament into the methanol coagulation bath at room temperature followed by soaking the filament in methanol to obtain the loaded security fiber free of HFIP.
• Figure 1 depicts process of making Silk fiber/IR absorbing fiber UV fluorescence fiber through extrusion.
• Figure 2 depicts obtained strands of UV fluorescent silk fibers chopped in 3-5mm length.
• Figure 3 depicts optical image determining thickness of 150 microns for UV fluorescent silk fibers at the speed of 0.3ml/min.
• Figure 4 depicts cotton paper embedded with UV fluorescent silk fibers in visible light.
• Figure 5 depicts authentication of paper embedded with UV fluorescence [Sodium yttrium Fluoride-oxide doped with Ytterbium and Thulium (Na, Y, Yb, Tm) F4 material] silk fibers with human eye.
• Right side image shows Yellow-Red fluorescence at 365nm; whereas image to the left show Orange-Red fluorescence under UV lamp (254nm).
• Figure 6 depicts obtained strands of NIR absorbing silk fibers chopped in 3 -5mm length.
• Figure 7 depicts optical image determining thickness of IR absorbing silk fibers at two different injections Speed. At speed of 0.05ml/min fibers has thickness between 45-50 microns and at O.lml/min fibers has thickness between 75-85 microns.
• Figure 8 depicts cotton paper embedded with IR absorbing silk fibers in visible light.
• Figure 9 depicts authentication of paper embedded with IR absorbing (IR -895 dye) silk fibers using a digital camera capable of detecting IR light.
• Right side image shows blackening of fibers under NIR light as it contains NIR absorbing silk fibers; whereas image to the left does not show any kind of absorbance of NIR light.
• the present invention describes the loaded silk fibroin as security feature in the substrate to combat counterfeiting, wherein said loaded silk fibroin is embedded in to the substrate making it impossible for the frauders to replicate the technology and hence useful in counteracting counterfeiting.
• the present invention uses the luminophores and/or the IR fluorescent dyes advantageously as markers to provide security features to combat counterfeiting and prohibiting the replication of technology.
• the present invention relates to a security fiber comprising of silk fibroin loaded with markers selected from inorganic UV fluorescent chromophore and organic IR absorbing chromophore that can be identified on exposure to said spectral wavelength, wherein said security fiber is useful to combat counterfeiting.
• the UV fluorescence absorber is selected from inorganic material such as Sodium yttrium Fluoride-oxide doped with Ytterbium and Thalium.
• the NIR absorber is selected from organic dye IR-895, i.e. Dimethyl ⁇ 4-[l,7,7-tris(4-dimethylaminophenyl)-2,4,6- heptatrienylidene]-2,5-cyclohexadien-l-ylidene ⁇ ammonium perchlorate.
• the silk fiber is selected from natural silk fiber or regenerated silk fiber (RSF), preferably the silk fiber is RSF which imparts durability and toughness to the fiber.
• the fluorescent markers used in the present invention are substantially colourless.
• the UV fluorescent material can be excited at a wavelength 254 nm and 365 nm and IRIR absorber in the wavelenghth 890 nm.
• the marker is loaded in to the silk fibroin in the ratio of 0.1 wt/v %.
• the present invention relates to a process for preparing said security fiber through extrusion, wherein said markers are bulk loaded in to the silk fiber.
• the process for bulk loading the markers in to the silk fibroin to obtain security fiber comprises;
• step (1) mixing the fluorescent markers in to the silk solution of step (1), wherein the concentration of fluorescent marker varies from 0.1 to 10.0 w/v % depending upon the concentration of silk solution;
• the spinning may be carried out by wet spinning or electrospinning technique known in the art.
• the loaded silk fibers obtained are nano, milli or micron sized, preferably micro sized depending on the speed of extrusion.
• the thickness of the fibers is in the range of 10 microns to 200 microns, preferably in the range of 50 microns to 150 microns. Further these fibers were chopped in 3-5 mm length.
• the present invention relates to a substrate embedded security fiber wherein said security fiber comprises silk fibroin loaded with markers selected from inorganic UV fluorescent chromophore and organic IR absorbing chromophore useful to combat counterfeiting.
• the substrate is selected from the group consisting of textiles, fabrics, plastics and security paper such as bank note paper, passport paper, visa paper, fiduciary paper or labels, packaging materials and the like.
• the silk fiber is selected from natural silk fiber or regenerated silk fiber (RSF), preferably the silk fiber is RSF which imparts durability and toughness to the fiber.
• the markers are loaded in to the silk fibroin at a ratio of 0.1 w/v% UV fluorescent dye and 5 w/v% IR dye.
• the present invention provides a process for preparation of said security fiber through extrusion, wherein said markers are bulk loaded in to the silk fiber.
• the silk fibers obtained are nano, milli or micron sized, preferably micro sized.
• the concentration of loading material varies from 0.1 to 10.0 w/v % depending upon the concentration of silk solution.
• the loaded silk fibers are obtained by electrospinning technique.
• the thickness of fibers obtained by the electrospinning or extrusion technique is in the range of 10 microns to 200 microns, preferably 50 microns to 150 microns depending on the speed of extrusion or electrospinning.
• the present invention provides a substrate embedded security fiber wherein said security fiber comprises silk fibroin loaded with markers selected from UV fluorescent chromophore or IR absorbing chromophore.
• the substrate is selected from the group consisting of textiles, fabrics, plastics and security paper such as bank note paper, passport paper, visa paper, fiduciary paper or labels, packaging materials and the like
• the present invention relate to a security paper comprising cotton fibers and silk fibroin loaded with markers selected from inorganic UV fluorescent chromophore or organic IR absorbing chromophore; wherein said security feature is embedded in to the security paper.
• the present invention provides a process for embedding said security fiber into the paper comprising dissolving said security fiber loaded with markers into the slurry of paper pulp in suitable ratio of 0.15 w% to form a uniform dispersion, setting the dispersion on the mesh and drying the sheet of security paper embedded with silk fiber on the mesh by pressing.
• the present invention provides a method for authentication of articles/objects using such bulk loaded silk fibers comprising irradiating the security markers using UV light or using a digital camera capable of detecting IR light reflected from the surface of the article/object.
• the articles/objects comprises textiles, fabrics, plastics and security paper such as bank note paper, passport paper, visa paper, fiduciary paper or labels, packaging materials and the like.
• the present invention relate to a security paper comprising cotton fibers and silk fibroin loaded with markers selected from inorganic UV fluorescent chromophore and organic IR absorbing chromophore; wherein said security feature is embedded in to the security paper.
• the present invention relate to a process for embedding the security feature in to the paper comprising; dissolving security fiber loaded with markers of the present invention into the slurry of paper pulp in suitable ratio of 0.15 wt% to form a uniform dispersion, settling the dispersion on the mesh and press drying the sheet of security paper embedded with silk fiber on the mesh. Accordingly the process of loading the marker in to the silk fibroin to obtain loaded silk fibre as security element and further embedding said security element in to the paper is described herein below:
• RSF Regenerated Silk Fibroin
• HFIP Hexafiuoro-iso-propanol
• the obtained RSF solution is then mixed with loading material, such as IR absorbing dye, UV fluorescent chromophore, , wherein the concentration of loading material varies from 0.1 to 10.0 w/v % depending upon the concentration of RSF solution.
• loading material such as IR absorbing dye, UV fluorescent chromophore, wherein the concentration of loading material varies from 0.1 to 10.0 w/v % depending upon the concentration of RSF solution.
• the material is loaded in the bulk of the fiber (not on surface only), the 'loaded silk microfibers' is further extruded through a stainless steel spinneret with 0.45 mm inner diameter using syringe pump into the methanol coagulation bath at room temperature or the 'loaded silk microfibers' are drawn using electrospinning technique.
• the extruded filament is then soaked in the methanol bath over 3 h to allow the HFIP to diffuse from the fiber.
• the thickness of fibers obtained by the electrospinning or extrusion technique is in the range of 10 microns to 200 microns, preferably 50 microns to 150 microns depending on the speed of extrusion or electrospinning.
• the chopped, 'loaded silk microfibers' are mixed with the paper pulp, in the suitable ratio of 0.15 wt% i.e. 6-8 fibers in the pulp required to make 50X50 mm papers.
• the loaded silk fiber shows uniform dispersion with cotton fibers.
• the preparation of paper pulp from cotton fibers in water is as reported in the art.
• the paper embedded with security feature is obtained, wherein the surface feature is UV or IR absorbing dye' loaded silk fibroin microfibers', particularly the security paper made by the instant process comprises, mixture of cotton fiber and UV fluorescent chromophore loaded silk microfibers; or cotton fiber and IR absorbing chromophore loaded silk microfibers.
• the invention provides a method for authentication of article/ object embedded with security fiber comprising irradiating the loaded markers using UV light or or IR light and observing the reflected light from the surface of the article/object.
• the articles/objects can be selected from textiles, fabrics, plastics, security paper such as bank note paper, passport paper, visa paper, fiduciary paper or labels, packaging materials and the like. Accordingly, the authentication of paper embedded with UV fluorescent silk microfibers is irradiated using UV vapor lamp or other UV source and observing the colour change.
• Silk Fibers loaded with UV fluorescent chromophore shows Orange-Red color fluorescence which can be easily detected by human eye.
• the authentication of paper embedded with IR absorbing silk fibers is performed by irradiating said absorber with IR light.
• Silk Fibers loaded with IR absorbing chromophore shows black colour of fibers due to absorbance which can be easily detected using a digital camera capable of detecting IR light reflected from the surface of the paper.
• the present invention relates to the use of security fiber comprising silk fibroin loaded with markers selected from inorganic UV fluorescent chromophore or organic IR absorbing chromophore which can be identified on exposure to said wavelength for authentication of articles/ objects.
• the lyophilized silk sponge was dissolved in HFIP for 2 days, yielding a 12 w/v% solution.
• the HFIP solution was extruded through a stainless steel spinneret with 0.45 mm inner diameter using syringe pump into the methanol coagulation bath at room temperature ( 25°C).
• the extruded filament was soaked in the methanol bath over 3 h to allow the HFIP to diffuse from the fiber.
• the obtained fibers were 45-50 microns in thickness. Fibers were cut with the scissor in a fixed length of 3-5 mm approximately.
• Example 2 Preparation of Silk fibers using regenerated Silk in Hexafluoro-iso-propanol (HFIP) through Electrospinning
• the lyophilized silk sponge was dissolved in HFIP for 2 days, yielding a 12 w/v% solution.
• the HFIP solution was electrospun through an Electrospinning instrument consisting of stainless steel spinneret with 0.45 mm inner diameter, syringe pump and collector plate at room temperature (25°C). Thickness of the obtained fibers was found 100 nm - 1 micron. Further depending on the rate of infuse volume and spinneret inner diameter, fibers upto 30-35 microns were obtained. Obtained nano and micron size fibers were chopped in 3 -5mm length as given in example 1 .
• lyophilized silk sponge 90 mg was dissolved in 3 ml HFIP for 2 days, in order to get 3 w/v% of silk solution. This is followed by mixing 0.15 mg (5 w/v%) of Sodium yttrium Fluoride-oxide doped with Ytterbium and Thulium (Na, Y, Yb, Tm) F4 (UV fluorescent material, obtained from Global Nanotech, Catalouge no.
• UV fluroscent dye sodium yttriium fluroide-oxide doped with yttrium & thalium purchased from Global Nanotech, Mumbai is IOVV200
• a well dispersed UV fluorescent material silk solution was obtained.
• UV fluorescent silk fiber showed uniform dispersion with cotton fibers. Further the paper was made from the pulp as explained in example 5. Authentication of paper embedded with UV fluorescent silk fibers was done by observing the paper under UV lamp. Silk Fibers loaded with UV fluorescent chromophore showed Orange-Red color fluorescence which can be easily detected by human eye.
• Example 7
• the instant microfiber is made of silk fibroin, makes the current invention cost effective, also the said invisible markers are bulk loaded in the microfiber (not merely surface treated), which minimizes loss of fluorescence, lowers the risk of loss of security markers when substrate is exposed to chemical, solvent or other stimuli. Further, the invention provides novel security element that prohibits the forgers form replicating the technology.

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• 2015
  • 2015-01-05 WO PCT/IN2015/000003 patent/WO2015114649A1/en active Application Filing
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