GB2276883A - Optical material containing a liquid crystal - Google Patents

Optical material containing a liquid crystal Download PDF

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Publication number
GB2276883A
GB2276883A GB9307038A GB9307038A GB2276883A GB 2276883 A GB2276883 A GB 2276883A GB 9307038 A GB9307038 A GB 9307038A GB 9307038 A GB9307038 A GB 9307038A GB 2276883 A GB2276883 A GB 2276883A
Authority
GB
United Kingdom
Prior art keywords
liquid crystal
optical material
clcp
laminae
polymer
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.)
Withdrawn
Application number
GB9307038A
Other versions
GB9307038D0 (en
Inventor
Ian Alexander Shanks
Christoph Dobrusskin
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
CENTRAL RESEARCH LAB Ltd
Central Research Laboratories Ltd
Original Assignee
CENTRAL RESEARCH LAB Ltd
Central Research Laboratories Ltd
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by CENTRAL RESEARCH LAB Ltd, Central Research Laboratories Ltd filed Critical CENTRAL RESEARCH LAB Ltd
Priority to GB9307038A priority Critical patent/GB2276883A/en
Publication of GB9307038D0 publication Critical patent/GB9307038D0/en
Publication of GB2276883A publication Critical patent/GB2276883A/en
Application status is Withdrawn legal-status Critical

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Classifications

    • CCHEMISTRY; METALLURGY
    • C09DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09DCOATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D11/00Inks
    • C09D11/02Printing inks
    • C09D11/03Printing inks characterised by features other than the chemical nature of the binder
    • C09D11/037Printing inks characterised by features other than the chemical nature of the binder characterised by the pigment
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61KPREPARATIONS FOR MEDICAL, DENTAL, OR TOILET PURPOSES
    • A61K8/00Cosmetics or similar toilet preparations
    • A61K8/02Cosmetics or similar toilet preparations characterised by special physical form
    • A61K8/0295Liquid crystals
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61QSPECIFIC USE OF COSMETICS OR SIMILAR TOILET PREPARATIONS
    • A61Q3/00Manicure or pedicure preparations
    • A61Q3/02Nail coatings
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B41PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41MPRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
    • B41M3/00Printing processes to produce particular kinds of printed work, e.g. patterns
    • B41M3/14Security printing
    • CCHEMISTRY; METALLURGY
    • C09DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09DCOATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D7/00Features of coating compositions, not provided for in group C09D5/00; Processes for incorporating ingredients in coating compositions
    • C09D7/40Additives
    • C09D7/70Additives characterised by shape, e.g. fibres, flakes or microspheres
    • CCHEMISTRY; METALLURGY
    • C09DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09KMATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K19/00Liquid crystal materials
    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08LCOMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L2205/00Polymer mixtures characterised by other features
    • C08L2205/14Polymer mixtures characterised by other features containing polymeric additives characterised by shape
    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08LCOMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L67/00Compositions of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Compositions of derivatives of such polymers

Abstract

An optical material comprises laminae of an aligned chiral liquid crystal or chiral liquid crystal polymer (1) which is a solid at room temperature, and a light transmissive medium such as nail vanish (2). The may be constituted by layers of a chiral liquid crystal polymer on flakes of a different material such as a polymer or aluminium. The material may be used in, cosmetics, paints, and inks for security marking documents. <IMAGE>

Description

OPTICAL MATERIAL This invention relates to optical material comprising particles of a liquid crystal material in a light transmissive medium. Such optical material may be used in ink for security marking documents. A known optical material is disclosed, for example, in Australian patent AU-488662.

Cholesteric liquid crystals (CLCs) and cholestelic liquid crystal polymers (CLCPs) exhibit circular dicliroic properties in their aligned state. This means they have the ability to separate incident unpolarized white light into a narrow wavelength band of circularly polarized light which is reflected, whilst transmitting the rest of the light (i.e.

white light minus one circular polarization state in the narrow wavelength band). A typical transmission characteristic of such an aligned CLC is shown in figure 1 of the accompanying drawings, which shows a graph of percentage transmission versus wavelength for a red cholesteric liquid crystal. Different materials are used to produce different senses of circular polarization.

The wavelength at which maximum reflection (or minimum transmission) occurs can be chosen to lie anywhere in the near ultra-violet (us), visible or infrared (IR) parts of the electromagnetic spectrum by suitable choice of CLC or CLCP pitch. For a specific CLC or CLCP, the wavelength (X) of peak reflection and the width (a) of the narrow wavelength band are determined by the formulae: A, = n.p = = hip where n is the average refractive index of the CLC or CLCP, An is the birefringence of the CLC or CLCP, and p is the helical pitch of the layer of CLC or CLCP. Cholesteric liquid crystals are also flown as chiral nematics. Similar optical properties will be observed for chiral smectic liquid crystals and chiral smectic liquid crystal polymers.

In tlle optical material disclosed in Australian patent AU488662, the particles are small capsules of a CLC in its liquid state, together with a light transmissive medium.

The thennochromic properties of this material are used to make inks for documents of value. Such an optical material has a number of disadvantages including poor colour purity and brightness, restricted viewhlg angles if the polarization properties of the reflected light are to be preserved, susceptibility to damage during high pressure printing, and the inability of the capsules to be given particular shapes.

An alternative way to make a security element for a banknote is disclosed in Canadian patent CA-2032587, in which a solid CLCP in the form of a thread or a 2 dimensional film laminated to the baiiknote is used. This has disadvantages associated with thread manufacture and film lamination. Also such an element may not survive frequent folding.

An object of the present invention is to enable these disadvantages to be mitigated.

According to the invention there is provided an optical material comprising particles of a liquid crystal material in a light transmissive medium, characterized in that the particles are laminae of a chiral liquid crystal which has an oriented form and which is a solid at room temperature.

The liquid crystal may be a high melting point cholesteric or chiral smectic liquid crystal, or a cholesteric or chiral smectic liquid crystal polymer. The medium may be, for example, a liquid, gel or soft solid.

Embodiments of the invention will now be described, by means of example only, with reference to the accompanying diagrammatic drawings in which: Figure 1 shows the transmission characteristic versus wavelength for a red cholesteric liquid crystal material discussed hereinbefore, Figure 2 shows a first embodiment in the form of a niixture of CLCP laminae and a light transmissive medium provided on a surface, Figure 3 shows a second embodiment in the form of sequential layers each of a mixture of CLCP flakes and a substantially transparent medium provided on a surface, Figure 4 shows in cross-section an optical material including polymer particles coated with a layer of CLCP and a light transniissive medium.

In the first embodiment shown in figure 2 an optical material including laminae 1 of a solid cholesteric liquid crystal polymer and a light transmissive medium 2 is provided as a cosmetic on the surface of a person's fingemail 3 to give an iridescent pattern. In this embodhnent the medium 2 is transparent nail varnish, and the laniinae are in the form of small flakes. Two types of CLCP flake are present, specifically flakes of Wacker LC-Silicone CC3767 (red) and flakes of CC3939 (blue) cross-linked polymer respectively, these polymers being obtainable from "Consortium fur Electrochemische llldustrie" of Munich, Germany.The major dimensions of the flakes are approximately 200 microns by 100 microns and they are approximately 10 microns thick; the flakes make up 20% of the mixture by weight.

The flakes 1 of CLCP are made in the following way. Two clean glass plates with optically flat surfaces are coated with a thin layer of nylon by spin coating. These layers are rubbed with a velvet or silk cloth to provide a layer to align the mesogenic groups (this technique is well flown for Liquid Crystal Display manufacture). Two self adhesive tape spacers 50 microns thick are provided at opposite edges of a major surface of each plate, and a solution of 32 parts of the un-crosslillked CLCP in 66 parts toluene with 2 parts initiator is applied and spread evenly across the plates using a doctor blade or squeegee supported by the spacers. The tape spacers are removed from the glass plates and the plates are then placed side by side in a vacuum oven to drive off the solvent.The plates are then placed with the CLCP coatings facing one another with small pillar spacers at each corner between tlle plates. These spacers are sucll that they melt or deform at a predetermined temperature (in this case 85"C), and are sized so as to leave a clear air gap between the two CLCP coated surfaces before the spacers deform.

This assembly is put in a bag sealer and encapsulated in a plastic bag from which the air is removed so that the CLCP coated surfaces face one another with no air between. This assembly is then put into a fumace at a temperature of 850C. This melts the pillars so that the CLCP plates move towards one another. The CLCP also softens so that a film with flat surfaces aligned by the nylon coating is formed between the plates. The assembly is then exposed to UV radiation at this elevated temperature to cross-link the polymer. The assembly is then allowed to cool, after which it is removed from the bag and prised apart. It is usual for portions of the area of the film (having the full layer thickness of approximately 10 microns) to adhere to each plate at this stage. Flakes of the polymer are then scraped off the plates using a hard instrument, and further ground with an agate mortar and pestle if required.

Optical materials with different properties may be formed by using different ratios of CLCP weight to medium weight. Mixtures with CLCP content as low as 0.5% may have a speckled appearance, wllereas mixtures with CLCP content as high as 80% can be used to give a glittering metallic appearance. In use, when such optical material is applied to a surface, the flakes tend to lie in the plane of the surface and show strong iridescent colours. The colour effects produced by CLCPs are durable as they are not due to dyes but rather due to a structured matrix of molecules. Thus a surface coated with such a material may be sanded down and itself coated with a transparent lacquer to improve the colour effects or surface smoothness.

In the second embodiment shown in figure 3, two inks (a) and (b) are made up using: (a) particles of CLCP consisting of flakes 4 of Wacker LC-Silicone CC3767 (red) crosslinked and aligned, made as described above, together with an epoxy binder acting as a substantially transparent medium 7, (b) particles of CLCP consisting of flakes 5 of Wacker LC-Silicone CC3939 (blue) crosslinked and aligned, made as described above, together with an epoxy binder acting as a substantially transparent medium 11, which may be identical to the medium 7.

These inks are printed and cured sequentially as successive layers on the surface 6 of a document. The flakes constitute 15% by weight of the inks prior to printing. In applications such as inks for banktrotes and documents of value an elastomeric light transmissive medium which acts as a binder or contains an additional binder is preferably used so that the material can survive folding and/or abrasion of the document. One such material is RTV 615 A silicone resin and curing agent supplied by GE Silicones, 4500 AC Bergen op Zoom, the Netherlands.

Although in the embodiments described above CLCPs are used for the laminae, flakes of a high melting point cholesteric liquid crystal which has an oriented fonn and which is a solid at room temperature may be used as an alternative. Such laminae may be formed by quenching the aligned CLC rapidly in liquid nitrogen to fonn a glass, and then grinding this glass in an agate mortar and pestle whilst it is still cold. Chiral smectic liquid crystals may also be used as an altemanve.

The third embodiment shown in figure 4 takes the form of flakes 8 of a black coloured base polysiloxane polymer coated on each side with a layer 9 of an aligned polysiloxane CLCP in an epoxy resin 10 which acts as a light transillissive medium and binder. In this figure the flakes are shown in cross-section. Forming the flakes in this way enables colour effects to be obtained which may be stronger and less dependent on the colour of any background or the colour of the light transmissive medium or other component of the mixture.

More than one layer of CLCP may be applied to the base polymer, and each layer need not be applied to the whole surface of the polymer particle. Base polymers other than polysiloxane may be used, for example dyed mylar or PVA. The particles need not be coloured black. Stronger colour effects may be produced if a particle is given a specific colour, and a layer of CLCP which reflects light of the same colour and one sense of circular polarization is provided thereon. The effect may be enhanced if the particle is provided with a second layer of a CLCP which reflects light of substantially the same colour with the opposite sense of circular polarization to that of the first layer and which at least partially overlaps the first layer.

The particles need not be of a polymer, and may be provided with a reflective surface under the CLCP layer. For example, particles of aluminium or mica may be used with one or more CLCP layers thereon. The particles or laminae do not have to be planar. Concave or convex particles or laminae may be employed to produce iridescence with an apparent depth different from the thickness of the laminae.

Other light transmissive media such as petroleum jelly, amyl acetate, cellulose acetate butyrate + methyl ethyl ketone, polyvinyl alcohol + water, or polyurethane lacquer may be used as an alternative in any of the above embodiments. Coloured substantially transparent media may be used as another alternative. For the coating to retain the polarization properties of the flakes the medium or binders chosen should be free from birefringence. However, decorative effects may still be obtained even if a birefringent medium is used.

Although specific Lw crosslinkable cholesteric liquid crystal polysiloxane polymers have been described in the above embodjinents, many other types of CLCP such as, for example, polyacrylates may be used as an alternative. Specifically the polymers need not be Lw crosslinkable. Chiral smectic liquid crystal polymers may be used as an alternative. Similarly the method of manufacture described is not the only way to make such flakes - polymer films with such good surface quality are not always necessary, and for some applications coated drums or flexible plastic sheeting or aluminium foil may be used in the manufacture in place of the glass plates. Flake dimensions from a few microns across to hundreds of microns may be used for different effects.

Optical materials may be formed using laminae with a single reflection characteristic. Optical materials may also be formed using mixtures of laminae with different reflection characteristics. Laminate may also be made each with a plurality of narrow wavelength reflection bands and one or more senses of circular polarization by using multiple layers. Materials may be made using mixtures of laminae reflecting in the same narrow wavelength band but different senses of circular polarization. Such laminae will reflect approximately 50% of unpolarized incident light in a specified narrow wavelength band, but almost 100% in that band where they overlap.

The reflection pattem of the coated surface is in general random and unique, as in general the reflective particles are randomly dispersed within the medium and of random size. Each pattern may be optically read in the manner of a fingerprint and may be difficult to falsify. The surfaces of the particles themselves may be arranged to have an identifiable structure, such as an interference layer (for example a 1/4 wave plate) or a diffraction grating or hologram which can diffract incident light to give additional iridescent colours. Such a grating or hologram may be coated with a further transparent layer (for example of indium tin oxide) to enhance the diffraction efficiency by increasing the change in refractive index between the surface of the lamina and the medium.The reflection characteristics from a multiplicity of such lamina disposed randomly may give a pattern similar to an X-ray powder diffraction pattern with characteristic rings which can be used to identify the optical material present. Sudi a pattern may also be obtained by rotating an object such as a CD marked with the optical material. The reflection characteristics may be used to code information. The codes may be read by inspecting through a circular or linear polarizer. Many combinations of flakes with different colours and polarization characteristics are possible. The colour effects are particularly suitable for document and banknote printing as the reflection characteristics cannot be reproduced photographically. UV or IR reflecting laminae may be used for security printing applications as such patterns need not be visible to the naked eye. "Hidden" patterns may be made by printing an area with a material with a specific colour and regions within that area with different senses of polarization of the reflected light. The pattern will then only be seen by viewing tluough a polarizer.A silllilar effect may be obtained by using regions with reflection characteristics which reflect different amounts at a specific wavelength but appear the same colour to the eye. The pattern may then be viewed using light of the specific wavelength to produce a pattern which would not be visible using a broad band light source.

The optical materials described above have many uses. For example they may be used to protect credit cards or CDs or documents of value such as banknotes from counterfeiting. Iridescent decorative effects may be produced for car paints, cosmetics including nail vanish, eye shadow, lipstick etc. Lw reflecting flakes may be used to make sun screen products. Such optical materials together with abrasives may be used in facial scrubs. Lastly, printing the materials onto textiles enables interesting decorative effects to be obtained.

Claims (10)

1. An optical material comprising particles of a liquid crystal material in a light transmissive medium, characterized in that the particles are laminae of a chiral liquid crystal which has an oriented form and which is a solid at room temperature.
2. An optical material as claimed in claim 1 hl which the chiral liquid crystal is a chiral liquid crystal polymer.
3. An optical material as claimed in claim I in which the chiral liquid crystal is a cholesteric liquid crystal.
4. An optical material as claimed in claim 2 in which the polymer is a cholesteric liquid crystal polymer.
5. An optical material as claimed in claim 2 or 4 wherein the laminae are constituted by a layer on particles of a different material.
6. An optical material as claimed in claim 5 in which the laminae comprise a plurality of layers each layer having a different reflection characteristic.
7. An optical material as claimed in any of claims 1 - 6 in which some laminate have different reflection characteristics to others.
8. An optical material as claimed in any of claims 1 - 7 in which the light transmissive medium is coloured.
9. A paint, ink, security marking agent, or cosmetic including an optical material as claimed in any of claims 1 - 8.
10. An optical material substantially as described herein with reference to figure 2 or figure 3 or figure 4 of the accompanying drawings.
GB9307038A 1993-04-05 1993-04-05 Optical material containing a liquid crystal Withdrawn GB2276883A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB9307038A GB2276883A (en) 1993-04-05 1993-04-05 Optical material containing a liquid crystal

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
GB9307038A GB2276883A (en) 1993-04-05 1993-04-05 Optical material containing a liquid crystal
EP94912013A EP0693098A1 (en) 1993-04-05 1994-03-30 Optical material
PCT/GB1994/000664 WO1994022976A1 (en) 1993-04-05 1994-03-30 Optical material
AU64335/94A AU6433594A (en) 1993-04-05 1994-03-30 Optical material

Publications (2)

Publication Number Publication Date
GB9307038D0 GB9307038D0 (en) 1993-05-26
GB2276883A true GB2276883A (en) 1994-10-12

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Family Applications (1)

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GB9307038A Withdrawn GB2276883A (en) 1993-04-05 1993-04-05 Optical material containing a liquid crystal

Country Status (4)

Country Link
EP (1) EP0693098A1 (en)
AU (1) AU6433594A (en)
GB (1) GB2276883A (en)
WO (1) WO1994022976A1 (en)

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WO1995032247A1 (en) * 1994-05-24 1995-11-30 Daimler-Benz Aktiengesellschaft Effect lacquer and lacquering, in particular for car bodies, by means of liquid crystal interference pigments
WO1996002597A2 (en) * 1994-11-23 1996-02-01 Basf Aktiengesellschaft Process for coating and printing substrates
WO1997030136A1 (en) * 1996-02-15 1997-08-21 Merck Patent Gmbh Cholesteric flakes
EP0872336A2 (en) * 1997-04-17 1998-10-21 Clariant GmbH Polymer laminate with improved covering
WO1999011719A1 (en) * 1997-09-02 1999-03-11 Basf Aktiengesellschaft Multilayer cholesteric pigments
WO1999011733A1 (en) * 1997-09-02 1999-03-11 Basf Aktiengesellschaft Coatings with a cholesteric effect and method for the production thereof
EP0911758A2 (en) * 1997-07-29 1999-04-28 Nhk Spring Co.Ltd. Optical identification system using cholesteric liquid crystals
WO1999057223A1 (en) * 1998-05-06 1999-11-11 Basf Aktiengesellschaft Multilayer cholesteric pigments
EP0994775A1 (en) * 1997-07-09 2000-04-26 Reveo, Inc. Coloring media having improved brightness and color characteristics
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US6665042B1 (en) 2000-05-16 2003-12-16 The University Of Rochester Electrically switchable polymer liquid crystal and polymer birefringent flake in fluid host systems and optical devices utilizing same
WO2004005425A1 (en) * 2002-07-06 2004-01-15 Merck Patent Gmbh Flakes comprising non-chiral liquid crystal material
US6753044B2 (en) 1991-11-27 2004-06-22 Reveo, Inc. Coloring media having improved brightness and color characteristics
WO2004104685A1 (en) * 2003-05-20 2004-12-02 The University Of Rochester Electrically addressable optical devices using a system of composite layered flakes suspended in a fluid host to obtain angularly dependent optical effects
WO2006006854A2 (en) * 2004-07-13 2006-01-19 Stichting Dutch Polymer Institute Microstructuring of mesogens using contact printing
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US7042617B2 (en) 2003-04-02 2006-05-09 The University Of Rochester Optical devices having flakes suspended in a host fluid to provide a flake/fluid system providing flakes with angularly dependent optical properties in response to an alternating current electric field due to the dielectric properties of the system
EP1710604A1 (en) * 2005-04-06 2006-10-11 JDS Uniphase Corporation High chroma optically variable color-shifting glitter
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Cited By (51)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6753044B2 (en) 1991-11-27 2004-06-22 Reveo, Inc. Coloring media having improved brightness and color characteristics
WO1995032247A1 (en) * 1994-05-24 1995-11-30 Daimler-Benz Aktiengesellschaft Effect lacquer and lacquering, in particular for car bodies, by means of liquid crystal interference pigments
WO1996002597A3 (en) * 1994-11-23 1996-05-23 Basf Ag Process for coating and printing substrates
US5798147A (en) * 1994-11-23 1998-08-25 Basf Aktiengesellschaft Process for coating and printing substrates
WO1996002597A2 (en) * 1994-11-23 1996-02-01 Basf Aktiengesellschaft Process for coating and printing substrates
US6404464B1 (en) 1995-10-30 2002-06-11 Reveo, Inc. Method and system for producing color images with improved brightness and color characteristics on radiation absorptive surfaces
WO1997030136A1 (en) * 1996-02-15 1997-08-21 Merck Patent Gmbh Cholesteric flakes
US6414092B1 (en) 1996-02-15 2002-07-02 Merck Patent Gesellschaft Mit Beschraenkter Haftung Cholesteric flakes
EP1132451A1 (en) * 1996-02-15 2001-09-12 MERCK PATENT GmbH Choleristic flakes
US6207770B1 (en) 1996-02-15 2001-03-27 Merck Patent Gmbh Cholesteric flakes
EP0872336A2 (en) * 1997-04-17 1998-10-21 Clariant GmbH Polymer laminate with improved covering
EP0872336A3 (en) * 1997-04-17 1999-03-03 Clariant GmbH Polymer laminate with improved covering
US6143379A (en) * 1997-04-17 2000-11-07 Clariant Gmbh Polymer laminates having increased hiding power
EP0994775A1 (en) * 1997-07-09 2000-04-26 Reveo, Inc. Coloring media having improved brightness and color characteristics
EP0994775A4 (en) * 1997-07-09 2003-04-02 Reveo Inc Coloring media having improved brightness and color characteristics
EP0911758A3 (en) * 1997-07-29 2003-03-26 Nhk Spring Co.Ltd. Optical identification system using cholesteric liquid crystals
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WO1994022976A1 (en) 1994-10-13
AU6433594A (en) 1994-10-24
GB9307038D0 (en) 1993-05-26
EP0693098A1 (en) 1996-01-24

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