EP1452338A1 - Caractéristiques de sécurité dichroiques à motifs - Google Patents

Caractéristiques de sécurité dichroiques à motifs Download PDF

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Publication number
EP1452338A1
EP1452338A1 EP03004494A EP03004494A EP1452338A1 EP 1452338 A1 EP1452338 A1 EP 1452338A1 EP 03004494 A EP03004494 A EP 03004494A EP 03004494 A EP03004494 A EP 03004494A EP 1452338 A1 EP1452338 A1 EP 1452338A1
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European Patent Office
Prior art keywords
vis
latent
preferentially
converted
phenylazo
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German (de)
English (en)
Inventor
Christoph Kocher
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Eidgenoessische Technische Hochschule Zurich ETHZ
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Eidgenoessische Technische Hochschule Zurich ETHZ
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Priority to EP03004494A priority Critical patent/EP1452338A1/fr
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    • 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
    • B42D25/20—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof characterised by a particular use or purpose
    • 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
    • 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
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H21/00—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties
    • D21H21/14—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties characterised by function or properties in or on the paper
    • D21H21/40—Agents facilitating proof of genuineness or preventing fraudulent alteration, e.g. for security paper
    • D21H21/44—Latent security elements, i.e. detectable or becoming apparent only by use of special verification or tampering devices or methods
    • D21H21/48—Elements suited for physical verification, e.g. by irradiation

Definitions

  • the present invention relates to novel security items as well as to a method for producing novel security items.
  • Light-polarizing elements produced from uniaxially oriented polymer films comprising dichroic dyes have been proposed as optical features for use in security applications (see for example US 3,391,479, H. O. Buzzell, P. F. Jordan, (Polaroid), "Laminations” and US 5,004,327, A. Rosén, (Svecia Antiqua Limited), "Light polarizing material in the form of sheets or of a web and a method for the manufacture of the material”).
  • the fact that the effect of anisotropic absorption observed in such uniaxially oriented materials comprising dichroic dyes cannot be photocopied nor mimicked by common printing techniques makes such systems of interest for optical security features.
  • this beneficial characteristic also hampers the production of visually attractive patterns and images displaying the desired dichroic effect.
  • the main aspect of the present invention is thus to provide methods that yield light-polarizing color patterns in uniaxially oriented polymer films.
  • the objective problem underlying the present invention is therefore to provide new polarizing security items which can for example be used for the protection of security documents. It additionally relates to a method for the production of such security items.
  • the present invention provides a new security item in that a security element is provided having at least one segment comprising at least one latent VIS absorber with linearly polarized absorption and/or linearly polarized emission.
  • latent VIS absorber has to be understood that this moiety is capable of being transformed into another moiety which acts as an absorber in the visible spectral range, i.e. in the range between 400nm up to 800nm. This other moiety shall be called converted VIS absorbing form.
  • the latent VIS absorber may preferentially itself already be an absorber in the visible spectral range, but it may also be a moiety which is transparent in the visible range of the electromagnetic spectrum, but for example absorbing in the UV or in the IR region. Such a latent VIS absorber can e.g. be converted either chemically or photo-chemically into its converted VIS absorbing form.
  • the converted VIS absorbing form shows linearly polarised absorption and/or emission.
  • the object of the present invention is therefore a product according to claim 1, and a process according to claim 17.
  • the key feature of the invention is therefore the fact that the provision of such a latent VIS absorber showing linearly polarised absorption and/or emission, which can be converted into the converted VIS absorbing form, usually showing different spectral characteristics than the latent VIS absorber, allows the provision of spatially resolved colour patterns whereby these patterns also have polarisation characteristics. Since such features cannot be easily copied and since such features can easily be verified by means of a simple polarisation filter or by means of polarised irradiation or a combination of these two methods, it provides a very effective means for securing documents like banknotes and the like.
  • the at least one latent VIS absorber is applied to or embedded in a matrix, which matrix is preferentially transparent for wavelengths in the visible region.
  • a matrix can for example be made of a polymer or a polymer blend.
  • the polymer is chosen from the group consisting of polyethylene (PE), in particular linear low-density polyethylene (LLDPE) or ultra-high molecular weight polyethylene (UHMW-PE), polyamide (PA), polypropylene (PP), polyethyleneterephthalate (PET), polycarbonate (PC), polyvinylalcohol (PVA1), polyvinylchloride (PVC), polyurethane (PU) and mixtures thereof.
  • PE polyethylene
  • LLDPE linear low-density polyethylene
  • UHMW-PE ultra-high molecular weight polyethylene
  • PA polyamide
  • PP polypropylene
  • PET polyethyleneterephthalate
  • PC polycarbonate
  • PVA1 polyvinylalcohol
  • PVC polyvinylchlor
  • such a matrix shows uniaxial orientation.
  • This uniaxial orientation can for example have been obtained by uniaxial stretching of the matrix with the embedded latent VIS absorber, wherein preferentially the drawing ratio (1/1 0 ) of the stretching is more than 2, even more preferentially above or equal to 4 or 8.
  • Such a uniaxial stretching of the matrix with the embedded latent VIS absorber leads to a molecular orientation not only of the matrix but also of the latent VIS absorber, provided that the molecular structure being used as the latent VIS absorber shows corresponding anisotropy.
  • such a security item is characterized in that the latent VIS absorber and/or its converted VIS absorbing form show a dichroic ratio of more than 2 in absorption and/or emission, preferentially a dichroic ratio of more than 5 in absorption and/or emission, and most preferentially a dichroic ratio of more that 10 or even more than 20 or 50.
  • the security item is characterised in that the latent absorber coloured in its pristine form (latent VIS absorber), wherein the colour of the pristine form differs from the one of the converted VIS absorbing form. If both forms are coloured in the visible range, particularly interesting optical effects can be achieved when the security item is either observed through a polarizer or is irradiated using linearly polarised light. This particularly so, if the latent VIS absorber is at least partially converted to its converted VIS absorbing form, wherein preferentially the VIS absorbing form is present in a spatially resolved manner.
  • adjacent patterns of the two forms are produced leading to a very distinct optical effect, in particular if more than one latent VIS absorber showing different colours in the pristine form and/or in the converted VIS absorbing form are employed, and if the different substances are arranged in a spatially resolved manner.
  • Another embodiment which leads to different effects if viewed under polarisation filters with different orientation or if irradiated with different polarisation directions can be achieved, if different layers with different directions of polarisation are provided adjacent to each other.
  • This can for example be done by providing at least two layers comprising latent VIS absorber, wherein the latent VIS absorbers are at least partially converted to their converted VIS absorbing forms in a spatially resolved manner, and wherein these layers comprise different latent VIS absorbers and/or show different orientation of the linear polarization, wherein preferentially there is two layers with orthogonal directions of polarization.
  • the two patterns of the two layers can be arranged to match each other to e.g. give rise to a flip flop effect when viewed under a rotating polarizer.
  • a security item according to the present invention is in a form selected from the group consisting of fibres, threads, strips, films, sheets, layers, tapes, plates, discs, chips and/or combinations thereof.
  • the conversion from the latent VIS absorber to the converted VIS absorbing form is possible using various routes.
  • this conversion can be achieved in a spatially resolved manner by using irradiation (for example UV, but also X-ray and the like as possible) or chemical treatment, preferentially by locally modifying the pH value, or a combination of these methods.
  • Postprocessing by for example applying heat or irradiation in another spectral range might be advantageous for stabilizing the system and for stopping the conversion process definitely.
  • the molecular structure used for the latent VIS absorber or for the converted VIS absorbing form is a dichroic rod-like molecule, the transition dipole moment of which preferentially substantially coincides with the geometrical long axis of the molecule.
  • a molecular structure allows the uniaxial alignment of these molecules within a matrix of a polymer which is drawn in one specific direction. The molecules can then give rise to an anisotropic absorption of the incident light consequently giving rise to the polarisation effects.
  • the conversion between the two forms can be made possible by providing particular groups that can be cleaved off chemically or photo-chemically.
  • One possibility is to provide the latent VIS absorber with at least one photo-labile and/or acid-labile chromogenic leaving group.
  • the latent VIS absorber and/or its converted VIS absorbing form is a derivative of Sudan Red B, or Dihydroxynaphthol, in particular (4-Phenylazo-phenylazo) derivatives thereof, or a mixture thereof, wherein these compounds are provided with at least one photo-labile and/or acid-labile chromogenic leaving group.
  • the latent VIS absorber is a Benzoic acid or a Boc derivative of Sudan Red B, of 1-(4-Phenylazo-phenylazo)-naphthalene-2,6-diol, of 6-alkyloxy-1-(4-Phenylazo-phenylazo)-naphthalene-2,6-diol (with the alkyl-group preferentially in the range of C1-C20), in particular of 6-dodecyloxy-1-(4-Phenylazo-phenylazo)-naphthalene-2,6-diol, of 4-(4-Phenylazo-phenylazo)-naphthalene-1,3-diol, or of 6-alkyloxy-4-(4-Phenylazo-phenylazo)-naphthalene-1,3-diol (with the alkyl-group preferentially in the range
  • the present invention also relates to a method of producing security items as they have been described above.
  • the method is basically characterised in that an object is provided with at least one security element having at least one segment comprising at least one latent VIS absorber with linearly polarized absorption and/or linearly polarized emission.
  • the converted VIS absorbing form shows linearly polarised absorption and/or linearly polarised emission, wherein the spectral properties of the two forms are different from each other to allow the desired effects.
  • the security element is produced by melt processing a polymeric substance or blend with a latent VIS absorber, forming a corresponding object like a fibre or film, and by subsequently drawing the object in one direction, preferentially using a draw ratio above 2, preferentially between 2 and 10, most preferentially between 4 and 8.
  • the latent VIS is preferentially at least partially converted to its converted VIS absorbing form by means of a chemical or photochemical process, if need be assisted by elevated temperature or followed by heat treatment, wherein preferably the conversion is carried out in a spatially resolved manner.
  • the conversion between the two forms can be achieved by using a photographic process, a lithographic process, a screen printing process, an inkjet printing process or a laser printing process. It can involve the chemical, preferentially acid-induced, or photo-chemical elimination of an element of the latent VIS absorber, preferentially by means of a photo-acid generator (PAG) and subsequent stabilization by evaporation of the photo-acid generator.
  • PAG photo-acid generator
  • the present invention provides systems and methodologies that yield patterned, light-polarizing features of increased mechanical and environmental stability.
  • the present invention provides a process for making uniaxially oriented polymer films displaying light-polarizing colour patterns by selectively converting uniaxially aligned chemical substances comprised in the oriented substrate into dichroic dyes aligned uniaxially within the oriented substrate.
  • the present invention provides a process for making uniaxially oriented polymer films displaying light-polarizing colour patterns by e.g. selectively converting uniaxially aligned dichroic pH-sensitive dyes from their deprotonated form into a differently coloured, protonated form by use of preferentially photochemically released acidic species, e.g. by employing so-called photo acid generators (PAG's).
  • PAG's photo acid generators
  • the present invention provides a process for making uniaxially oriented polymer films displaying light-polarizing colour patterns by selectively converting uniaxially aligned dichroic pH-sensitive dyes from their protonated form into a differently coloured, deprotonated form by use of preferentially photochemically released basic species, e.g. by employing so-called photo base generators.
  • the technology involves chromogenic dyes based on ortho-phenylazonaphthol-dyes (R. Kuhn, F. Bär, Ann., 1935, 516, 143) that were derivatized with cleavable protective groups. These caged species exist in an exclusive azo-configuration but upon cleavage of the caging group can release the respective tautomerizing ortho -phenylazonaphthol-dye (V. F. Traven, A. M. Tsygankova, B. L. Stepanov, Chem. Abstr., 1985, 103, 143344w; V. Bek á rek, K. Rothschein, P.
  • Sudan Red B a common azo-dye that is characterized by a long molecular axis ('rigid-rod'-type molecule) that coincides with the molecule's transition dipole moment.
  • Sudan Red B has already been used as active component in light-polarizing polymer sheets exhibiting appreciable dichroism (Y.
  • the compounds 2Bz and 2Boc are obtained accordingly, by employing 2,4-dihydroxynaphthol in the azo-coupling reaction).
  • the dihydroxy-naphthols were chosen for the azo-coupling reaction (H. Zollinger, Azo and Diazo Chemistry, Interscience Publishers, Inc., New York, 1961) to preferentially yield one single product which predominantly exists in the hydrazone form (E. F. Saad, E. A. Hamed, A. El-Faham, Spectroscopy Lett., 1996, 29 , 1047; A. Ly ka, Z. Vrba, M. Vrba, Dyes Pigments, 2000, 47 , 45) and thus allowing for a strong chromogenic behavior.
  • the dihydroxynaphthol-dyes 2a and 3a were subsequently etherified with one equivalent of bromododecane.
  • Column chromatography yielded the alkyloxy-substituted o-hydroxynaphthol diazo-dyes, which were subsequently converted to their chromogenic equivalents by introducing either the photo-labile benzoyl (Bz) group or the acid-labile tert -butoxycarbonyl ( t -Boc) group.
  • Bz photo-labile benzoyl
  • t -Boc acid-labile tert -butoxycarbonyl
  • the benzoyl-caged yellow-colored chromogenic dyes 1Bz, 2Bz and 3Bz could be reverted to their respective red-colored o -hydroxy-equivalents by simple exposure to short-wavelength UV light (see Figure 1).
  • the conversion was achieved by acid-catalyzed removal of the t-Boc group (cf. Figure 1).
  • Spatially resolved conversion in a lithographic process in this case can be achieved by employing photo acid generators (PAG's, E. Reichmanis, F. M. Houlihan, O. Nalamasu, T. X. Neenan, Chem.
  • the deprotection kinetics are highly temperature-dependent and are therefore commonly carried out in a post-exposure heat treatment which can be referred to as 'post-exposure bake'.
  • the PAG employed here was benzenesulfonic acid phenyl ester which is also used in microlithography.
  • the t-Boc-protected chromogenic dyes are also cleaved in absence of acid, but only at much higher temperatures well exceeding the processing temperatures employed for the production of the present LLDPE blend films. As revealed by thermal analysis, decomposition of these compounds occurs at temperatures exceeding 180 °C.
  • LLDPE blend films containing 1OH, 2OH, 3OH, 1Bz, 2Bz or 3Bz were processed at 180 °C; films containing the somewhat heat-sensitive compounds 1Boc, 2Boc or 3Boc were processed at 140 °C.
  • photo-acid generator benzenesulfonic acid phenyl ester was employed in a concentration of 3% w/w in blend films containing the acid-labile species 1Boc, 2Boc or 3Boc.
  • the isotropic melt-processed blend films were stretched at a temperature of up to 120 °C to a draw ratio ⁇ of 8.
  • Polarized absorption spectra principal spectral absorptions
  • p -polarized, 0°, A ⁇ the wave vector parallel
  • s-polarized, 90°, A ⁇ the stretching direction of the blend films.
  • DR A the dichroic ratio
  • Conversion of the photo-labile chromogenic dyes 1Bz, 2Bz and 3Bz was achieved by exposure to 254 nm UV light for time intervals up to 1 h.
  • the relatively long exposure times are related to the low intensity of the UV light source employed (340 ⁇ W/cm 2 ) and the reduced transparency of the matrix material of the relatively thick film samples at the employed wavelength (254 nm). It is obvious that optimization of these conditions can reduce the required exposure times into the seconds regime.
  • the acid-labile chromogenic dyes 1Boc, 2Boc and 3Boc were converted upon photoactivation of the PAG for 30 min with 254 nm UV light from a conventional lab-type UV lamp and subsequent post-exposure heat treatment at 100 °C for 1 h.
  • the characteristic absorption band of 1OH was restored.
  • the DR A measured for this absorption band amounted to 2.1, and is therewith, within the experimental error, comparable to the DR A of 2.4 of the unconverted system.
  • conversion was achieved by photoactivation of the PAG additionally contained in the film and subsequent post-exposure heat treatment.
  • the characteristic absorption band of 1OH was restored, and a DR A of 2.3 was measured in the absorption maximum, which again is similar to the DR A of 2.9 measured for the system prior to conversion.
  • Films comprising the uncaged dye 2OH were characterized by a deep-red color. In comparison with blend films comprising 1OH, these films exhibited a more intense, bluish-shade red hue.
  • the absorption maximum of 2OH in LLDPE was located at a somewhat longer wavelength than the one of 1OH, i.e. centered around 535 nm (see Table 1). This influence of an additional substituent in the 6-position of the naphthalene-system on the absorption properties is in accordance with results published on the mono-azo dye 4-phenylazo-3,7-diol (E. F. Saad, E. A. Hamed, A. El-Faham, Spectroscopy Lett., 1996, 29, 1047).
  • Stretched blend films comprising the alkoxy-substituted dye 2OH exhibit a DR A of 4.6, which is somewhat lower than the DR A of 5.3 observed for the unsubstituted dye 1OH.
  • Figure 3 shows the conversion of 2Bz comprised in a LLDPE film (0.2% w/w 2Bz , thickness 100 ⁇ m) upon irradiation with UV light (254 nm).
  • the inset shows the increase of the absorption corresponding to the released species 2OH (measured at 530 nm). Dots are measured absorption values, the curve represents a first order kinetics fit
  • the DR A of blend films comprising 2Bz and 2Boc was established to be 3.4 and 3.8, respectively. Compared to the chromogenic dyes 1Bz and 1Boc that do not bear a long alkoxy chain and exhibited DR A 's of 2.4 and 2.9, respectively, the dichroism in the dodecyloxy-substituted systems was clearly enhanced. The same is true for developed films of 2Bz and 2Boc. The dichroic ratio of a developed film of 2Bz was established as 2.6, and the DR A of a developed film of 2Boc remained at 3.8.
  • Blend films comprising the unprotected dye 3OH were characterized by an orange-red color and an absorption spectrum with a maximum at 491 nm.
  • the respective dotted lines represent the absorption perpendicular to the stretching direction (90°)).
  • the absorption band of blend films comprising the protected chromogenic dyes 3Bz and 3Boc were centered around 424 and 439 nm, respectively.
  • the bathochromic shift upon derivatization of 3OH was therewith less pronounced than in the previously discussed cases of systems 1 and 2, amounting to approximately 50 nm.
  • the DR A displayed by stretched blend films comprising 3OH was found to be as high as 25 at a draw ratio of 8.
  • the dichroic effect was therewith dramatically improved. Consequently, upon examining a stretched sample comprising 3OH through a rotating optical polarizer, the appearance of the film changed from orange-red to almost colorless, while in the case of samples comprising 1OH or 2OH, the red shade remained apparent to some extent when observing the sample through an optical polarizer with its optical axis aligned parallel to the stretching direction of the film.
  • the chromogenic derivative 3Bz of 3OH in a stretched LLDPE film displayed a DR A of only 3.3.
  • the developing absorption band exhibited a DR A of 3.7.
  • the detrimental effect of the rigid benzoyl group located in an off-center position to the long molecular axis becomes apparent.
  • the DR A of stretched blend films comprising 3Boc substituted with the more flexible t-Boc-group was determined as 7.2. Upon conversion of 3Boc, the absorption band of 3OH was restored.
  • Benzoic acid 1-(3-methyl-4- m -tolylazo-phenylazo)-naphthalen-2-yl ester (1Bz). 408.0 mg (1.1 mmol) of 1-(3-methyl-4- m -tolylazo-phenylazo)-naphthol were dissolved in 5 mL anhydrous pyridine. To the stirred mixture, 0.5 mL (0.7 g, 5.5 mmol) of benzoyl chloride were added. The mixture was heated to reflux and stirred for 2 h. Subsequently, the mixture was allowed to cool to room temperature, washed with water (3x 100 mL) and extracted with CH 2 Cl 2 (150 mL).
  • 6-dodecyloxy-1-(4-phenylazo-phenylazo)-naphthalen-2-ol (2OH).
  • An mixture of 504.0 mg (3.65 mmol) K 2 CO 3 and 5 mL of dimethylformamide were heated to 70 °C and stirred for 10 min under argon.
  • 302.2 mg (0.82 mmol) 2a were added and stirred for 10 min.
  • 208.3 mg (0.84 mmol) of 1-bromo-dodecane were added by the aid of a syringe.
  • the mixture was stirred for 3 h at 70 °C and subsequently cooled to room temperature and diluted with ca. 50 mL water.
  • Benzoic acid 6-dodecyloxy-1-(4-phenylazo-phenylazo)-naphthalen-2-yl ester (2Bz).
  • An amount of 106.9 mg (0.2 mmol) of 3a were dissolved in 10 mL pyridine.
  • 56.2 mg (0.4 mmol) benzoyl chloride were slowly added by the aid of a syringe.
  • the mixture was stirred for 2 h at reflux and subsequently cooled to room temperature, washed with water (3x 100 mL) and extracted with CH 2 Cl 2 (150 mL).
  • the organic layer was dried over MgSO 4 , filtered, and the solvents were evaporated.
  • the resulting solid was subjected to column chromatography (CH 2 Cl 2 , silica gel) to quantitatively yield the respective product (most mobile fraction) as dark orange solid. Mp 123 °C.
  • Benzoic acid 4-dodecyloxy-1-(4-phenylazo-phenylazo)-naphthalen-2-yl ester (3Bz). Reacting 93.9 mg (0.17 mmol) of 3OH with 38.5 mg (0.27 mmol) of benzoylchloride in 5 mL of pyridine according to the above procedure for 2Bz resulted 93.9 mg (1.47 mmol, 84% with respect to 3OH) of the product as brick-red solid. Mp 90 °C.
  • Blend films containing 0.2% w/w of the various dyes in LLDPE were produced as follows:
  • Blend films containing 0.2% w/w of the dyes in LLDPE were produced from a 1% w/w master batch, which was obtained by dissolving 5 mg of the respective dye in approx. 2 mL CH 2 Cl 2 and decorating 495 mg of LLDPE pellets with that solution. After evaporation of the solvent at ambient, the decorated pellets were pressed into a blend film between aluminum sheets in a hot press (Carver 2518) at a load of 8 tons and subsequently cooled in a cold press (Carver M) at the same load.
  • a hot press Carver 2518
  • Carver M cold press
  • the processing temperature was 180 °C
  • the processing temperature was reduced to 140 °C in order to prevent any undesired conversion of these somewhat heat-sensitive compounds.
  • the obtained blend films were cut into pieces, which were subsequently mixed and again processed into a film. This process was repeated four times in order to obtain a homogeneous distribution of the dyes within the polymer matrix. This 1% w/w blend film was then used as a master-batch to produce a 0.2% w/w blend film, by processing 100 mg of the 1% w/w blend film with 400 mg of LLDPE pellets, according to the above method.
  • the acid-labile systems were mounted to a constraining device and subjected to a post-exposure heat treatment at 100 °C for 1 h.
  • a blend film of 100 ⁇ m thickness containing 0.2% w/w of the photo-labile chromogenic dye 3Boc and 3% of PAG was used and exposed for 30 min to 254 nm UV light through a photomask obtained by inkjet printing of the desired image on a poly(vinylalcohol) film.
  • Pictures of the reproduced yellow/red picture were taken with a Leica DC200 digital camera mounted on a Leica MS5 microscope equipped with an optical linear polarizer.
  • the sample exhibiting the color-inverting symbol was made with two films containing 0.2% w/w of 2Boc and 3% of PAG according to the same procedure.
  • the two films were imprinted in a perpendicular fashion with the same photomask and superimposed on a supporting glass substrate in a perpendicular manner. Photographs were taken as described above with the optical linear polarizer at the different angles indicated in the context of Fig. 4.

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20080190808A1 (en) * 2005-04-15 2008-08-14 Arrow Coated Products Ltd. Self Destructive Irreversible Security Packaging Film
US8679376B2 (en) 2012-03-09 2014-03-25 Samsung Electronics Co., Ltd. Dichroic dye for use in polarizing film, polarizing film, and display device including the polarizing film
EP3059713A1 (fr) * 2010-10-05 2016-08-24 Bundesdruckerei GmbH Procede de verification de l'authenticite d'un document de securite et/ou de valeur
WO2017009494A1 (fr) * 2015-07-10 2017-01-19 Universidad Politecnica De Madrid Procédé et dispositif pour sécuriser des documents par génération de multiples images latentes réflexives et transmissives
CN107090192A (zh) * 2017-05-24 2017-08-25 上海贝通色彩科技有限公司 一种耐碱性分散染料组合物

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Publication number Priority date Publication date Assignee Title
US4826976A (en) * 1984-09-04 1989-05-02 Polaroid Corporation Color-shifted dyes with thermally unstable carbamate moiety comprising T-alkoxycarbonyl group
WO1996037369A1 (fr) * 1995-05-25 1996-11-28 Bicc Public Limited Company Procede de marquage d'un article
US5879855A (en) * 1993-11-22 1999-03-09 Ciba Specialty Chemicals Corporation Compositions for making structured color images and application thereof
WO2000019016A1 (fr) * 1998-09-25 2000-04-06 Landqart Papier de securite et autres articles de securite

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
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US9421575B2 (en) 2005-04-15 2016-08-23 Arrow Greentech Limited Self-destructive irreversible security packaging film
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CN107090192B (zh) * 2017-05-24 2018-08-03 上海贝通色彩科技有限公司 一种耐碱性分散染料组合物

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