CA2004423A1 - Security marking - Google Patents
Security markingInfo
- Publication number
- CA2004423A1 CA2004423A1 CA002004423A CA2004423A CA2004423A1 CA 2004423 A1 CA2004423 A1 CA 2004423A1 CA 002004423 A CA002004423 A CA 002004423A CA 2004423 A CA2004423 A CA 2004423A CA 2004423 A1 CA2004423 A1 CA 2004423A1
- Authority
- CA
- Canada
- Prior art keywords
- saturable absorber
- wavelength
- security mark
- photochromic compound
- absorber comprises
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
- 239000006096 absorbing agent Substances 0.000 claims abstract description 22
- 150000001875 compounds Chemical class 0.000 claims abstract description 14
- 238000010521 absorption reaction Methods 0.000 claims description 16
- 239000000126 substance Substances 0.000 claims description 15
- 238000000034 method Methods 0.000 claims description 11
- ZFXPBTZXYNIAJW-UHFFFAOYSA-N 4-[2-(2-phenylethenyl)phenyl]triazine Chemical compound C=1C=CC=CC=1C=CC1=CC=CC=C1C1=CC=NN=N1 ZFXPBTZXYNIAJW-UHFFFAOYSA-N 0.000 claims description 3
- 230000005281 excited state Effects 0.000 claims description 3
- 239000000990 laser dye Substances 0.000 claims description 3
- QKLPIYTUUFFRLV-UHFFFAOYSA-N 1,4-bis[2-(2-methylphenyl)ethenyl]benzene Chemical compound CC1=CC=CC=C1C=CC(C=C1)=CC=C1C=CC1=CC=CC=C1C QKLPIYTUUFFRLV-UHFFFAOYSA-N 0.000 claims 2
- 230000005283 ground state Effects 0.000 claims 2
- 230000002441 reversible effect Effects 0.000 claims 1
- 238000006243 chemical reaction Methods 0.000 abstract 1
- 239000000758 substrate Substances 0.000 description 5
- YXFVVABEGXRONW-UHFFFAOYSA-N Toluene Chemical compound CC1=CC=CC=C1 YXFVVABEGXRONW-UHFFFAOYSA-N 0.000 description 3
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 description 2
- 239000000975 dye Substances 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 229920003229 poly(methyl methacrylate) Polymers 0.000 description 2
- 229920000642 polymer Polymers 0.000 description 2
- 239000004926 polymethyl methacrylate Substances 0.000 description 2
- PEBXLTUWFWEWGV-UHFFFAOYSA-N 1-methyl-2-(2-phenylethenyl)benzene Chemical compound CC1=CC=CC=C1C=CC1=CC=CC=C1 PEBXLTUWFWEWGV-UHFFFAOYSA-N 0.000 description 1
- 101150034533 ATIC gene Proteins 0.000 description 1
- BSYNRYMUTXBXSQ-UHFFFAOYSA-N Aspirin Chemical compound CC(=O)OC1=CC=CC=C1C(O)=O BSYNRYMUTXBXSQ-UHFFFAOYSA-N 0.000 description 1
- 239000004215 Carbon black (E152) Substances 0.000 description 1
- 101100536354 Drosophila melanogaster tant gene Proteins 0.000 description 1
- 241001508691 Martes zibellina Species 0.000 description 1
- 241001163743 Perlodes Species 0.000 description 1
- 239000004952 Polyamide Substances 0.000 description 1
- 239000004698 Polyethylene Substances 0.000 description 1
- 239000004372 Polyvinyl alcohol Substances 0.000 description 1
- ZVNYJIZDIRKMBF-UHFFFAOYSA-N Vesnarinone Chemical compound C1=C(OC)C(OC)=CC=C1C(=O)N1CCN(C=2C=C3CCC(=O)NC3=CC=2)CC1 ZVNYJIZDIRKMBF-UHFFFAOYSA-N 0.000 description 1
- 150000001252 acrylic acid derivatives Chemical class 0.000 description 1
- 230000004913 activation Effects 0.000 description 1
- 229940125898 compound 5 Drugs 0.000 description 1
- 125000001495 ethyl group Chemical group [H]C([H])([H])C([H])([H])* 0.000 description 1
- 230000008020 evaporation Effects 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
- 239000000835 fiber Substances 0.000 description 1
- 239000000945 filler Substances 0.000 description 1
- 229930195733 hydrocarbon Natural products 0.000 description 1
- 150000002430 hydrocarbons Chemical class 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 239000003973 paint Substances 0.000 description 1
- 229920002647 polyamide Polymers 0.000 description 1
- 239000004417 polycarbonate Substances 0.000 description 1
- 229920000515 polycarbonate Polymers 0.000 description 1
- -1 polyethylene Polymers 0.000 description 1
- 229920000573 polyethylene Polymers 0.000 description 1
- 229920002451 polyvinyl alcohol Polymers 0.000 description 1
- 239000004800 polyvinyl chloride Substances 0.000 description 1
- 229920000915 polyvinyl chloride Polymers 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 241000894007 species Species 0.000 description 1
- 238000001228 spectrum Methods 0.000 description 1
- 229920002554 vinyl polymer Polymers 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
- B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
- B41M3/00—Printing processes to produce particular kinds of printed work, e.g. patterns
- B41M3/14—Security printing
- B41M3/144—Security printing using fluorescent, luminescent or iridescent effects
-
- 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
-
- 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
- B42D25/40—Manufacture
- B42D25/405—Marking
-
- 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
-
- 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
Landscapes
- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Manufacturing & Machinery (AREA)
- Materials Engineering (AREA)
- Organic Chemistry (AREA)
- Non-Silver Salt Photosensitive Materials And Non-Silver Salt Photography (AREA)
- Electrochromic Elements, Electrophoresis, Or Variable Reflection Or Absorption Elements (AREA)
- Thermal Transfer Or Thermal Recording In General (AREA)
Abstract
ABSTRACT
A security mark has a photochromic compound covered by a controlled absorbtion layer comprising a saturable absorber. Light of a wavelength serbing to convert the photochromic compound is at low intensity absorbed by the saturable absorber. A photochromic compound converted by UV can thus be sunlight protected. At high intensities, the absorbtion of the saturable absorber drops to permit conversion of the photochromic compound
A security mark has a photochromic compound covered by a controlled absorbtion layer comprising a saturable absorber. Light of a wavelength serbing to convert the photochromic compound is at low intensity absorbed by the saturable absorber. A photochromic compound converted by UV can thus be sunlight protected. At high intensities, the absorbtion of the saturable absorber drops to permit conversion of the photochromic compound
Description
2(~ 3 - ~
.
SECUR}TY MAFXTNG ' ' ; -Ihis invention relates to security markin6 and in pareicular to the ~ -~
use of marking substances which include a pho~och~o~ic c~mPou~d. These substances can be arranged to take a colourless ~orm when applied So an article requiring authentication, ~or e~a~Ple a persanal identification document. The photochromic compound can be conver~ed to ~ coloured form by irradlation ~ith W, the opcically detectable colour change in the markin~ substance then serving to authentlCate the document.
Security markin~ substancec as outl~ned above are known ~nd reference is directed by way of exa~ple to W0 88/06306; JP 62227194 and WO 88/01288.
. :., . ;~
It is known that exposure to W over a perlod of time can destroY the photo~hromic effect ~n cert~n co~pounds. The life of a particular ~arking substance will depend UPon the flu~ of W eo which it is ; ;~
subjected ~hether durlng the authene~catlon procedure or extraneously.
The W pplled durin~ the authentication step is liable eo be a critical factor in deter~ining the ll~e of a marking subseance only in the case o~ ite~s r quiring very frequent authenelcation. E~traneou4 W froo sunlight will b~ an i~po~tant f~ctor in many cases ~here no control can be exerclsed over the m~nner in which the ~rked iten is stored.
. ~ .
It is one object of t~is inv-ntion to provide s method of ~rkin~
offerin~ increa~ed lifeti~es.
~ .' . ' . ~:~ ' ..
In applications where a relatively hidh de~ree of secusity is required, it would b~ adv~ntageous to provide a oore demanding ~uthentic~ion step, prefer~bly without sign~ficantl~ incre~sins the co~plexity of the authentic~tion apparstus. It is ehus a f~rther ob~ect of the present invention eo provide an i~proved ~ethod of markin6 oPfer~ng closor control over the e~sential require~onts of the auehentication stcp.
, .' ,'' ~ '.-`
' ~': ,' . . ' , ..,: : . ..
, , . . . , .. .. ~, , . , : . ~ . . , .,: . .. . .
Z~)4~3 .
.
Accordingly, the present invention con~istg in one aspec~ in a ~ethod of ~arking an ite~ with.. a security mark ~hich exhibit~ ~ ~eversible and opticRlly detectable ch~nge on e~posure to l;ght of a specific wavelength, co~pr$sing the steps of applying to the art~cle a ~arking sub~tance comprising a photochro~ic coopound convert~ble ~rom ~ne photochro~e t~ another on exposure to light o~ said wavelength, said co~pound ~eing covered by 8 controlled absorption layer cont~ning a sstursble absorber at said wavelength, whereby there is defined a threshold intensity of lieht at said wavelength bene~th wh~ch ~ :
threshold thore is ~y ~eason o~ absorption in said controlled absorption layer no detectable chsnge In the mark within a given time Per$od, a detectable change occuring substantially immediately at intensities above said threshold. : :::
~ '''.
Preferably, the saturable absorber comprises a laser dye having at s8id wavelength sn absorbtion cross section in the excited state whiCh . . . .
small compared with ehe absorbtioa cross section in the gro~nd ~tate. .
In another respeCt, the present invention consis~ in a security cark CO~prising 8 body 0~ oarking substance Cocprising a photochromic oo~pouna 8nd a sunlight protection lay~r covering said ~arkin~
9ubstanco, the sunli~ht protection layer comprisin~ a saturable ;:~
ab80rber.
It should be reco~nised th~t the te~m ~light~ as ~sod herein is not to b~ rogarded a9 restrietod to v~sible li6ht.
A variety of saturab~e absorber compound5 ~re known. They have the property that below a ehr~shola lighe Snt~nsity, ~n equilibrium is -~
e~tablished betw~ n moleculgr processes of photon absorptioa and relaxation, such Shat th~ transmissivity at the specific wavelen~th of ;~
operat~on is very low. Above the threshold Sntensity, the photon ~bsorption process ~s saturated. with 11 absorber ~olecule~ being : .
held ~n the h~eher en~rgy st~te. Above this threçhold inten5itY.
therefore, the substance has gi~n$~C4nt t~an4~S5ivitY at the specif~c wa~elensth.
- . .
2~ 4~3 ~ ~ .
Saturable absorbers are known `for use ~s h~gh speed swit~he~ in l~ers i~
~nd reference ~s directed in tA~s re~ard to ~Lasers - Lipe ~3pl~fiers and oscill~tors~ - D~eter ~oss - 1969 Acade~lc Press. . :~
}n the practice o~ the present invention, lt can be arranged, by appropriate selection o~ a saturable absorber and the eoncentration and thickness of the controlled sbsorPtion laye~, that ehe - .
transmissivity o~ the ~ayer to W at norn~ ight inten~ieie~ i9 -~
very low but ehat at a UV intensity achievable - ulth careful design -in authentication apparstw , the t~nsoissivity is high. ; ~ ..
The invention will ~ow be desc~lbed by w~y of exa~ple with reference to the accompanyin~ drawings in which~
Flgure 1 i~ a di~gra~tlc section throu8h a secu~ty mark in accordance with this invention, and .
Flgure 2 ls a diagra~atic sect~on thrvugh an alternative security nark accord~ng to thls inv~ntio~
Ref~rrlng to F16ur~ 1. a ~arklng subst~nce 10 is applied to a substrate 12 by printin~ or any other suitable ~pplication technique. ;
The marking ~ubstance includes a photochromic coopound which is pr ferably a ~ulgide but whlch could tak~ other forms such a~
splropyran, Thc detailed 5tructure o~ the photodhrvmic compound ~orm$
no part of the preseQt invention ~nd it will suf~ice to ~ake re~renc~
to the known ~re, ex4sples Or wh~ch a~ GB-A-1 464 603, GB-A-2 002 752 .
~nd GB-A-Z 051 813, The photochromic compound is incorporated ln the oarking ~ubstance by any of a ~ariety o~ appropr~te technigue~. For e~ample, the photochrom~c co3pound may be dissol~e~ or disperset in a solution of polymer~c material which is cast, eoated or otherwise ~pplied to the -~
substrate. For exa~ple, a photochromic fulg~de can ~e dissol~ed in a -~
solutlon o~ cell~lo~e ~cotate ~n acetone wi~h a fil~ Or the ~arking ~';'; ' ',''''''"''.,'.,''','`'''''', : :' ~' :,. . ,.'-~. ::
~ -. ,:, :- . .
.: . .: ., : . , ~ i .
: : : ~ : ::
Z1~4~3 ~ ~ ~
substance being fo~med upon evaporation of scetone; Alter*stive polymers are polyeste~s e.g. polyethylene terePhthPlate; acrylates, e.g. PMMA; ole~in poly~ers or co-poly~Qrs: vinyl polymers. e.t. P~A or PV~; polycarbonates and polyamides. Alternative organic sol~ents are toluene And chlorinsted hydroC~rbons.
In the illustrated example, ~he mark~ng substance 10 co~prises a 2.5%
concentratton of the photochromic Fulgide Aberchrome 540 (a~ailable fro~ Aberchro~ics Li~ited, ¢ard~ff) in PMMA cast from a solution ~n ethyl acetaeo. The for~ed security ~ark h~s an area of 1 sq C3 and the ~`
thickness o~ the ~arking substance is 5 uicrons. ;~
There is provided over the marking substance 10 a controlled absorption layer l4. This eo~prises a 10% concentration o~ a saturable absorber in an sppropriate ~atrlx s~ch as polyvinyl alcohol. In th$s exa~ple the saturabl~ absorber oolecule is triazinyl stilbene. For detailed in~ormat$on concerning the proproperties of this known satur~ble absorbe~. reference io dir~cted to textbooks such as ~Laser Dy~s ~ Properties o~ oryanic co~pounds for dye lasers~ - Mitsuo M~eda 1987 AcQdenic Press, ospoc~ally Sable 20. The thickness of the controllod absorption layer i~ 5 microns and it is calc~lat~d th~t ~t noroal sunlight intensities of UV, the controll d absorption layer ~ ~ -will dec~e~se th~ x of W incident upon the na~kiing substance by f~ctor o~ 1~2. ;;~
In tho ~uthentication step, the security nark i~ irradiat~d with high ~ ;
intensity W so as to convert the photoch~o~ic co pound to a coloured ~ n ~or~. ~hi~ chi~n6ing colour nay be observed visually. The intensity o~
UV e~ployod in the activation ~tep is in ~xcess of thc ~hreshold ~t which the 8aturable absorber i~iisaturate~. mug at an inten5ity of ;~
15 kw suitably focussed, the cont~olled absorption layer has ~
trans~iss~vity of ~pproxi~ate~y 80%. me high intensity UV may be prcvlded. for examplc, by a rlashlR~p with appropr~ate focusing, or other hieh intens$ty puls~d llght sourCQS.
: .: :
~.
.
2(~4a~3 . ~,, , ~he use of a saturable absorber ~n thë ma~ner accord~ng to thls ~ -~
invention has the adva~tage that the liPeti~e o~ the secur~tY mark on exposu~e to sunlight is substantially increased. ~owever, the -controlled absorption layer has little effect upon visible - for example, green or red - lig~t so that the photochro~c compound can be ret~rned rspidly to i S colourless for~ by irradiatlon at the appropriate w~velen~th. This can be done by exposure to sunllght ~r ~
another white li~ht Qource~ S~nce the trans~i~s~vitY of the controlled - ~ d absorption layer ~s relatively high above the threshold intensity, the . ; :
ti~e taken to colour the security mark in the actlvation step is not substantially increased.
In a modification, illustrated in Fi~ure 2, 8 base coat 16 is interposed between the markin~ substance 10 and the substrate 12. This bsse coat ~y t~pic~lly co~prlse a one to two micron layer of polyvinyl chloride which se~ves to enhance optical contrast and to protect the photochromic compound from poss~bly ds~sgin~ effeces of the substrate. The ~se of suc~ a base coat would, for exa~ple. be $mportant in the csse of paper or other fibre based substrates h8ving relatively high moisture level~ and containing fillers and other reaCt~nts having a pos~ibly doleterious ef~ect upon the photochro~ic conpound.
It should be under~tood that th$s invention has been described by way `~
of exa~ple only and a var~ety of modi~ications ~re poss~ble without depart~ng fro~ the scopa o~ the inv~nt~on.
Other s~turable 8bsorbers cgn be eoploy~d and the~e can be provided in .
a controlled absorption layer in a variety of tochniques. ~ne exa~ple o~ an alternative saturablo absorber ~olecule useful with fulgide photochroucs ~s 1,4-~is (o-methylstyryl) benzene. Th1s c~n be for3ed ~,~
~-: :. ,.: . . :: . :
as a sCr~en ink using a hydrocarbon sol~ent.
.: ;,, ~
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. . . :
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2(~4~3 ., ^
The wavelength band of 360 to 390mm is appropriate for a wide range of ~:
photochromic fulgides. Beyond ehe speci~ic saturable sb~orbers ment~oned, it will be posgible to employ a ran~e of lasor dyes absorbiny in the wa~elength range o~ interest and having ~n absorPtion cross section in the excited seate which is s~ll coopared to th~t mn the ~round s~a~e and thu~ bein~ capable of saturation. Reference is dir~ct~d in this r~rd to M~4d~ f~f~ ~n~ tn ~n~hnnk nf :
fl~ore~cent spectra of aromstic molecules~ Isador Berl~an - 19 Academic iress. ;
It is not necessary for the entire secur~ty mark to be co~ered b~ a single, contiguous controll~d absorption layer; separate block~ of the ~arking substance may be covered by respecei~e controlled absorption layers. The marking subst~nce need not be a poly~eric film it cay t8ke the form of. for exa~Ple, a paint or ink cont~inin~ a photochromic compo~nd or may in apProPriate cases consist of a photochromic compound alone.
~ :
.
SECUR}TY MAFXTNG ' ' ; -Ihis invention relates to security markin6 and in pareicular to the ~ -~
use of marking substances which include a pho~och~o~ic c~mPou~d. These substances can be arranged to take a colourless ~orm when applied So an article requiring authentication, ~or e~a~Ple a persanal identification document. The photochromic compound can be conver~ed to ~ coloured form by irradlation ~ith W, the opcically detectable colour change in the markin~ substance then serving to authentlCate the document.
Security markin~ substancec as outl~ned above are known ~nd reference is directed by way of exa~ple to W0 88/06306; JP 62227194 and WO 88/01288.
. :., . ;~
It is known that exposure to W over a perlod of time can destroY the photo~hromic effect ~n cert~n co~pounds. The life of a particular ~arking substance will depend UPon the flu~ of W eo which it is ; ;~
subjected ~hether durlng the authene~catlon procedure or extraneously.
The W pplled durin~ the authentication step is liable eo be a critical factor in deter~ining the ll~e of a marking subseance only in the case o~ ite~s r quiring very frequent authenelcation. E~traneou4 W froo sunlight will b~ an i~po~tant f~ctor in many cases ~here no control can be exerclsed over the m~nner in which the ~rked iten is stored.
. ~ .
It is one object of t~is inv-ntion to provide s method of ~rkin~
offerin~ increa~ed lifeti~es.
~ .' . ' . ~:~ ' ..
In applications where a relatively hidh de~ree of secusity is required, it would b~ adv~ntageous to provide a oore demanding ~uthentic~ion step, prefer~bly without sign~ficantl~ incre~sins the co~plexity of the authentic~tion apparstus. It is ehus a f~rther ob~ect of the present invention eo provide an i~proved ~ethod of markin6 oPfer~ng closor control over the e~sential require~onts of the auehentication stcp.
, .' ,'' ~ '.-`
' ~': ,' . . ' , ..,: : . ..
, , . . . , .. .. ~, , . , : . ~ . . , .,: . .. . .
Z~)4~3 .
.
Accordingly, the present invention con~istg in one aspec~ in a ~ethod of ~arking an ite~ with.. a security mark ~hich exhibit~ ~ ~eversible and opticRlly detectable ch~nge on e~posure to l;ght of a specific wavelength, co~pr$sing the steps of applying to the art~cle a ~arking sub~tance comprising a photochro~ic coopound convert~ble ~rom ~ne photochro~e t~ another on exposure to light o~ said wavelength, said co~pound ~eing covered by 8 controlled absorption layer cont~ning a sstursble absorber at said wavelength, whereby there is defined a threshold intensity of lieht at said wavelength bene~th wh~ch ~ :
threshold thore is ~y ~eason o~ absorption in said controlled absorption layer no detectable chsnge In the mark within a given time Per$od, a detectable change occuring substantially immediately at intensities above said threshold. : :::
~ '''.
Preferably, the saturable absorber comprises a laser dye having at s8id wavelength sn absorbtion cross section in the excited state whiCh . . . .
small compared with ehe absorbtioa cross section in the gro~nd ~tate. .
In another respeCt, the present invention consis~ in a security cark CO~prising 8 body 0~ oarking substance Cocprising a photochromic oo~pouna 8nd a sunlight protection lay~r covering said ~arkin~
9ubstanco, the sunli~ht protection layer comprisin~ a saturable ;:~
ab80rber.
It should be reco~nised th~t the te~m ~light~ as ~sod herein is not to b~ rogarded a9 restrietod to v~sible li6ht.
A variety of saturab~e absorber compound5 ~re known. They have the property that below a ehr~shola lighe Snt~nsity, ~n equilibrium is -~
e~tablished betw~ n moleculgr processes of photon absorptioa and relaxation, such Shat th~ transmissivity at the specific wavelen~th of ;~
operat~on is very low. Above the threshold Sntensity, the photon ~bsorption process ~s saturated. with 11 absorber ~olecule~ being : .
held ~n the h~eher en~rgy st~te. Above this threçhold inten5itY.
therefore, the substance has gi~n$~C4nt t~an4~S5ivitY at the specif~c wa~elensth.
- . .
2~ 4~3 ~ ~ .
Saturable absorbers are known `for use ~s h~gh speed swit~he~ in l~ers i~
~nd reference ~s directed in tA~s re~ard to ~Lasers - Lipe ~3pl~fiers and oscill~tors~ - D~eter ~oss - 1969 Acade~lc Press. . :~
}n the practice o~ the present invention, lt can be arranged, by appropriate selection o~ a saturable absorber and the eoncentration and thickness of the controlled sbsorPtion laye~, that ehe - .
transmissivity o~ the ~ayer to W at norn~ ight inten~ieie~ i9 -~
very low but ehat at a UV intensity achievable - ulth careful design -in authentication apparstw , the t~nsoissivity is high. ; ~ ..
The invention will ~ow be desc~lbed by w~y of exa~ple with reference to the accompanyin~ drawings in which~
Flgure 1 i~ a di~gra~tlc section throu8h a secu~ty mark in accordance with this invention, and .
Flgure 2 ls a diagra~atic sect~on thrvugh an alternative security nark accord~ng to thls inv~ntio~
Ref~rrlng to F16ur~ 1. a ~arklng subst~nce 10 is applied to a substrate 12 by printin~ or any other suitable ~pplication technique. ;
The marking ~ubstance includes a photochromic coopound which is pr ferably a ~ulgide but whlch could tak~ other forms such a~
splropyran, Thc detailed 5tructure o~ the photodhrvmic compound ~orm$
no part of the preseQt invention ~nd it will suf~ice to ~ake re~renc~
to the known ~re, ex4sples Or wh~ch a~ GB-A-1 464 603, GB-A-2 002 752 .
~nd GB-A-Z 051 813, The photochromic compound is incorporated ln the oarking ~ubstance by any of a ~ariety o~ appropr~te technigue~. For e~ample, the photochrom~c co3pound may be dissol~e~ or disperset in a solution of polymer~c material which is cast, eoated or otherwise ~pplied to the -~
substrate. For exa~ple, a photochromic fulg~de can ~e dissol~ed in a -~
solutlon o~ cell~lo~e ~cotate ~n acetone wi~h a fil~ Or the ~arking ~';'; ' ',''''''"''.,'.,''','`'''''', : :' ~' :,. . ,.'-~. ::
~ -. ,:, :- . .
.: . .: ., : . , ~ i .
: : : ~ : ::
Z1~4~3 ~ ~ ~
substance being fo~med upon evaporation of scetone; Alter*stive polymers are polyeste~s e.g. polyethylene terePhthPlate; acrylates, e.g. PMMA; ole~in poly~ers or co-poly~Qrs: vinyl polymers. e.t. P~A or PV~; polycarbonates and polyamides. Alternative organic sol~ents are toluene And chlorinsted hydroC~rbons.
In the illustrated example, ~he mark~ng substance 10 co~prises a 2.5%
concentratton of the photochromic Fulgide Aberchrome 540 (a~ailable fro~ Aberchro~ics Li~ited, ¢ard~ff) in PMMA cast from a solution ~n ethyl acetaeo. The for~ed security ~ark h~s an area of 1 sq C3 and the ~`
thickness o~ the ~arking substance is 5 uicrons. ;~
There is provided over the marking substance 10 a controlled absorption layer l4. This eo~prises a 10% concentration o~ a saturable absorber in an sppropriate ~atrlx s~ch as polyvinyl alcohol. In th$s exa~ple the saturabl~ absorber oolecule is triazinyl stilbene. For detailed in~ormat$on concerning the proproperties of this known satur~ble absorbe~. reference io dir~cted to textbooks such as ~Laser Dy~s ~ Properties o~ oryanic co~pounds for dye lasers~ - Mitsuo M~eda 1987 AcQdenic Press, ospoc~ally Sable 20. The thickness of the controllod absorption layer i~ 5 microns and it is calc~lat~d th~t ~t noroal sunlight intensities of UV, the controll d absorption layer ~ ~ -will dec~e~se th~ x of W incident upon the na~kiing substance by f~ctor o~ 1~2. ;;~
In tho ~uthentication step, the security nark i~ irradiat~d with high ~ ;
intensity W so as to convert the photoch~o~ic co pound to a coloured ~ n ~or~. ~hi~ chi~n6ing colour nay be observed visually. The intensity o~
UV e~ployod in the activation ~tep is in ~xcess of thc ~hreshold ~t which the 8aturable absorber i~iisaturate~. mug at an inten5ity of ;~
15 kw suitably focussed, the cont~olled absorption layer has ~
trans~iss~vity of ~pproxi~ate~y 80%. me high intensity UV may be prcvlded. for examplc, by a rlashlR~p with appropr~ate focusing, or other hieh intens$ty puls~d llght sourCQS.
: .: :
~.
.
2(~4a~3 . ~,, , ~he use of a saturable absorber ~n thë ma~ner accord~ng to thls ~ -~
invention has the adva~tage that the liPeti~e o~ the secur~tY mark on exposu~e to sunlight is substantially increased. ~owever, the -controlled absorption layer has little effect upon visible - for example, green or red - lig~t so that the photochro~c compound can be ret~rned rspidly to i S colourless for~ by irradiatlon at the appropriate w~velen~th. This can be done by exposure to sunllght ~r ~
another white li~ht Qource~ S~nce the trans~i~s~vitY of the controlled - ~ d absorption layer ~s relatively high above the threshold intensity, the . ; :
ti~e taken to colour the security mark in the actlvation step is not substantially increased.
In a modification, illustrated in Fi~ure 2, 8 base coat 16 is interposed between the markin~ substance 10 and the substrate 12. This bsse coat ~y t~pic~lly co~prlse a one to two micron layer of polyvinyl chloride which se~ves to enhance optical contrast and to protect the photochromic compound from poss~bly ds~sgin~ effeces of the substrate. The ~se of suc~ a base coat would, for exa~ple. be $mportant in the csse of paper or other fibre based substrates h8ving relatively high moisture level~ and containing fillers and other reaCt~nts having a pos~ibly doleterious ef~ect upon the photochro~ic conpound.
It should be under~tood that th$s invention has been described by way `~
of exa~ple only and a var~ety of modi~ications ~re poss~ble without depart~ng fro~ the scopa o~ the inv~nt~on.
Other s~turable 8bsorbers cgn be eoploy~d and the~e can be provided in .
a controlled absorption layer in a variety of tochniques. ~ne exa~ple o~ an alternative saturablo absorber ~olecule useful with fulgide photochroucs ~s 1,4-~is (o-methylstyryl) benzene. Th1s c~n be for3ed ~,~
~-: :. ,.: . . :: . :
as a sCr~en ink using a hydrocarbon sol~ent.
.: ;,, ~
.. .. . ......
':' ~,: ,:;;
' :...: "
. . . :
- :-' ~ : ~
2(~4~3 ., ^
The wavelength band of 360 to 390mm is appropriate for a wide range of ~:
photochromic fulgides. Beyond ehe speci~ic saturable sb~orbers ment~oned, it will be posgible to employ a ran~e of lasor dyes absorbiny in the wa~elength range o~ interest and having ~n absorPtion cross section in the excited seate which is s~ll coopared to th~t mn the ~round s~a~e and thu~ bein~ capable of saturation. Reference is dir~ct~d in this r~rd to M~4d~ f~f~ ~n~ tn ~n~hnnk nf :
fl~ore~cent spectra of aromstic molecules~ Isador Berl~an - 19 Academic iress. ;
It is not necessary for the entire secur~ty mark to be co~ered b~ a single, contiguous controll~d absorption layer; separate block~ of the ~arking substance may be covered by respecei~e controlled absorption layers. The marking subst~nce need not be a poly~eric film it cay t8ke the form of. for exa~Ple, a paint or ink cont~inin~ a photochromic compo~nd or may in apProPriate cases consist of a photochromic compound alone.
~ :
Claims (10)
1. A method of marking an item with a security mark which exhibits a reversible and optically detectable change. on exposure to light of a specific wavelength, comprising the steps of applying to the article a marking stance comprising a photochromic compound convertible from one photochrome to another on exposure to light of said wavelength, said compound being covered by a controlled absorption layer containing a saturable absorber at said wavelength, whereby there is defined a threshold intensity of light at said wavelength beneath which threshold there is by reason of absorption in said controlled absorption layer no detectable change in the mark within a given time period, a detectable change occuring substantially immediately at intensities above said threshold.
2. A method according to Claim 1, wherein the saturable absorber comprises a laser dye having at said wavelength an absorbtion cross section in the excited state which is small compared with the absorbtion cross section in the ground state.
3. A method according to Claim 1, wherein the saturable absorber comprises triazinyl stilbene.
4. A method according to Claim 1, wherein the saturable absorber comprises 1,4-Bis(o-methylstyryl)benzene.
5. A method according to any one of the preceding claims, wherein the photochromic compound comprises a fulgide.
6. A security Mark formed by the method of any one of the preceding claims.
- ? -
- ? -
7. A security mark comprising a body of marking substance comprising a photochromic compound and a sunlight protection layer covering said marking substance, the sunlight protection layer comprising a UV
saturable absorber.
saturable absorber.
8. A security mark according to Claim 7, wherein the saturable absorber comprises a laser dye having a UV absorbtion cross section in the excited state which is small compared with the absorbtion cross section in the ground state.
9. A security mark according to Claim 7, wherein the saturable absorber comprises triazinyl stilbene.
10. A security mark according to Claim 7, wherein the saturable absorber comprises 1,4-Bis(o-methylstyryl)benzene.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB888828091A GB8828091D0 (en) | 1988-12-01 | 1988-12-01 | Security marking |
| GB8828091.2 | 1988-12-01 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2004423A1 true CA2004423A1 (en) | 1990-06-01 |
Family
ID=10647806
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002004423A Abandoned CA2004423A1 (en) | 1988-12-01 | 1989-12-01 | Security marking |
Country Status (6)
| Country | Link |
|---|---|
| AU (1) | AU4744790A (en) |
| CA (1) | CA2004423A1 (en) |
| GB (1) | GB8828091D0 (en) |
| IL (1) | IL92524A0 (en) |
| WO (1) | WO1990006539A1 (en) |
| ZA (1) | ZA899183B (en) |
Families Citing this family (14)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| AU651876B2 (en) * | 1991-04-17 | 1994-08-04 | J.S. Mcmillan Printing Group | A printing process |
| US5289547A (en) * | 1991-12-06 | 1994-02-22 | Ppg Industries, Inc. | Authenticating method |
| US5330686A (en) * | 1992-08-19 | 1994-07-19 | Ppg Industries, Inc. | Temperature stable and sunlight protected photochromic articles |
| DE19836813A1 (en) | 1998-08-14 | 2000-02-24 | Bundesdruckerei Gmbh | Value and security document with optically stimulable dyes for authenticity testing |
| US6552290B1 (en) | 1999-02-08 | 2003-04-22 | Spectra Systems Corporation | Optically-based methods and apparatus for performing sorting coding and authentication using a gain medium that provides a narrowband emission |
| EP1038690A1 (en) * | 1999-03-22 | 2000-09-27 | Fabriques De Tabac Reunies S.A. | Printed latent raster image |
| DE19961841A1 (en) * | 1999-12-21 | 2001-06-28 | Joergen Brosow | Fraud-proof data carrier useful for security, e.g. banknote or check, contains photochromic substance converted from one stable isomer to another by light, embedded in substrate transmitting conversion and read-out light |
| FI116949B (en) | 2004-09-10 | 2006-04-13 | Stora Enso Oyj | Method of marking the material, marking the material and verifying the authenticity of the product |
| GB0708692D0 (en) | 2007-05-04 | 2007-06-13 | Innovia Films Ltd | Seelable, pealable film |
| US9822229B2 (en) | 2007-05-24 | 2017-11-21 | Innovia Films Limited | Low emissivity film |
| GB0714418D0 (en) | 2007-07-24 | 2007-09-05 | Innovia Films Ltd | UV barrier film |
| GB0714419D0 (en) * | 2007-07-24 | 2007-09-05 | Innovia Films Ltd | Indicia means |
| FR2927840B1 (en) * | 2008-02-25 | 2016-01-22 | Oberthur Technologies | "DOCUMENT COMPRISING A SECURITY MARK WITH VARIABLE VISUAL PERCEPTION" |
| EP3149106A4 (en) * | 2014-05-30 | 2018-01-17 | Cabela's Incorporated | System and method for application of chromic compositions |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2927025A (en) * | 1956-10-23 | 1960-03-01 | Ibm | Photosensitive materials and recording media |
| GB2104504B (en) * | 1981-07-16 | 1985-05-09 | English Clays Lovering Pochin | Stabilisation of photochromic fulgides and fulgimides |
| CA1268034A (en) * | 1985-01-31 | 1990-04-24 | Nori Y.C. Chu | Photochromic composition resistant to fatigue |
| JPS62108245A (en) * | 1985-11-06 | 1987-05-19 | Res Dev Corp Of Japan | Photochromic material, photochromic element, and process for recording and erasing information |
| EP0241247A3 (en) * | 1986-04-07 | 1988-04-27 | RAYCHEM CORPORATION (a Delaware corporation) | Reversible temperature indicating compositions |
| GB8703400D0 (en) * | 1987-02-13 | 1987-03-18 | Courtaulds Plc | Security marking |
-
1988
- 1988-12-01 GB GB888828091A patent/GB8828091D0/en active Pending
-
1989
- 1989-12-01 CA CA002004423A patent/CA2004423A1/en not_active Abandoned
- 1989-12-01 WO PCT/GB1989/001443 patent/WO1990006539A1/en unknown
- 1989-12-01 IL IL92524A patent/IL92524A0/en unknown
- 1989-12-01 ZA ZA899183A patent/ZA899183B/en unknown
- 1989-12-01 AU AU47447/90A patent/AU4744790A/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| ZA899183B (en) | 1991-09-25 |
| WO1990006539A1 (en) | 1990-06-14 |
| GB8828091D0 (en) | 1989-01-05 |
| AU4744790A (en) | 1990-06-26 |
| IL92524A0 (en) | 1990-08-31 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued |