EP0693098A1 - Optical material - Google Patents
Optical materialInfo
- Publication number
- EP0693098A1 EP0693098A1 EP94912013A EP94912013A EP0693098A1 EP 0693098 A1 EP0693098 A1 EP 0693098A1 EP 94912013 A EP94912013 A EP 94912013A EP 94912013 A EP94912013 A EP 94912013A EP 0693098 A1 EP0693098 A1 EP 0693098A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- liquid crystal
- optical material
- laminae
- clcp
- flakes
- 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- Withdrawn
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09D—COATING 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
- C09D11/00—Inks
- C09D11/02—Printing inks
- C09D11/03—Printing inks characterised by features other than the chemical nature of the binder
- C09D11/037—Printing inks characterised by features other than the chemical nature of the binder characterised by the pigment
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
- A61K8/00—Cosmetics or similar toiletry preparations
- A61K8/02—Cosmetics or similar toiletry preparations characterised by special physical form
- A61K8/0295—Liquid crystals
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61Q—SPECIFIC USE OF COSMETICS OR SIMILAR TOILETRY PREPARATIONS
- A61Q3/00—Manicure or pedicure preparations
- A61Q3/02—Nail coatings
-
- 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
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09D—COATING 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
- C09D5/00—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes
- C09D5/004—Reflecting paints; Signal paints
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09D—COATING 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
- C09D7/00—Features of coating compositions, not provided for in group C09D5/00; Processes for incorporating ingredients in coating compositions
- C09D7/40—Additives
- C09D7/65—Additives macromolecular
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09D—COATING 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
- C09D7/00—Features of coating compositions, not provided for in group C09D5/00; Processes for incorporating ingredients in coating compositions
- C09D7/40—Additives
- C09D7/70—Additives characterised by shape, e.g. fibres, flakes or microspheres
-
- 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
- C09K19/00—Liquid crystal materials
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L2205/00—Polymer mixtures characterised by other features
- C08L2205/14—Polymer mixtures characterised by other features containing polymeric additives characterised by shape
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L67/00—Compositions of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Compositions of derivatives of such polymers
Definitions
- This invention relates to optical material comprising particles of a liquid crystal material in a light transmissive medium.
- optical material may be used, for example, in ink for security marking documents.
- CLCs Cholesteric liquid crystals
- CLCPs cholesteric liquid crystal polymers
- FIG. 1 of the accompanying drawings 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 (UV), visible or infrared (IR) parts of the electromagnetic spectrum by suitable choice of CLC or CLCP pitch.
- UV near ultra-violet
- IR infrared
- the wavelength ( ⁇ ) of peak reflection and the width ( ⁇ ) of the narrow wavelength band are determined by the formulae:-
- n is the average refractive index of the CLC or CLCP
- ⁇ n is the birefringence of the CLC or CLCP
- p is the helical pitch of the layer of CLC or CLCP.
- Cholesteric liquid crystals are also known as chiral nematics. Similar optical properties will be observed for chiral smectic liquid crystals and chiral smectic liquid crystal polymers.
- the particles are small capsules of a CLC in its liquid state, together with a light transmissive medium.
- the thermochromic 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 viewing 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 object of the present invention is to enable these disadvantages to be mitigated.
- 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.
- This material has the advantage of a small temperature dependence of the colour, ability to withstand high pressure printing, and difficulty in reproducing the colours photographically for security applications.
- 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.
- 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 mixture 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 transmissive medium.
- an optical material including laminae 1 of a sohd cholesteric liquid crystal polymer and a light transmissive medium 2 is provided as a cosmetic on the surface of a person's fingernail 3 to give an iridescent pattern.
- the medium 2 is transparent nail varnish
- the laminae 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 Industrie" 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 known 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 33 parts of the un-crosslinked CLCP in 66 parts toluene with 1 part photo-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 the plates. These spacers are such 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 furnace at a temperature of 85°C. 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 (other temperatures such as for example 70°C, or even room temperature for blue material, may be used as an alternative).
- 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. Other grinding techniques such as ball milling or triple roll milling or ultrasonic agitation may be used as an alternative.
- 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, whereas mixtures with CLCP content as high as 80% can be used to give a glittering metallic appearance.
- CLCPs 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.
- 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.
- 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.
- 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.
- RTV 615 A silicone resin and curing agent supplied by GE Silicones, 4500 AC Bergen op Zoom, the Netherlands.
- CLCPs are used for the laminae
- flakes of a high melting point cholesteric liquid crystal which has an oriented form 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 form 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 alternative.
- 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 transmissive medium and binder.
- 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 d e 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.
- 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.
- 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.
- the medium or binders chosen should be free from birefringence. However, decorative effects may still be obtained even if a birefringent medium is used.
- UV crosslinkable cholesteric liquid crystal polysiloxane polymers have been described in the above embodiments, many other types of CLCP such as, for example, polyacrylates may be used as an alternative. Specifically the polymers need not be UV 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. Laminae 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 pattern 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 Such 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 through a polarizer. A similar 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.
- 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 varnish, eye shadow, lipstick etc. UV 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.
Landscapes
- Chemical & Material Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Organic Chemistry (AREA)
- Wood Science & Technology (AREA)
- Health & Medical Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Animal Behavior & Ethology (AREA)
- General Health & Medical Sciences (AREA)
- Public Health (AREA)
- Veterinary Medicine (AREA)
- Birds (AREA)
- Epidemiology (AREA)
- Liquid Crystal (AREA)
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 varnish (2). The laminae 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.
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, for example, in ink for security marking documents.
Cholesteric liquid crystals (CLCs) and cholesteric liquid crystal polymers (CLCPs) exhibit circular dichroic 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 (UV), 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 (λ) of peak reflection and the width (Δλ) of the narrow wavelength band are determined by the formulae:-
λ = n.p Δλ = Δn.p
where n is the average refractive index of the CLC or CLCP, Δn 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 known as chiral nematics. Similar optical properties will be observed for chiral smectic liquid crystals and chiral smectic liquid crystal polymers.
In a known optical material disclosed in Australian patent AU-488662, the particles are small capsules of a CLC in its liquid state, together with a light transmissive medium. The thermochromic 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 viewing 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 banknote 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. This material has the advantage of a small temperature dependence of the colour, ability to withstand high pressure printing, and difficulty in reproducing the colours photographically for security applications.
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 way 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 mixture 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 transmissive medium.
In the first embodiment shown in figure 2 an optical material including laminae 1 of a sohd cholesteric liquid crystal polymer and a light transmissive medium 2 is provided as a cosmetic on the surface of a person's fingernail 3 to give an iridescent pattern. In this embodiment the medium 2 is transparent nail varnish, and the laminae
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 Industrie" 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 known 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 33 parts of the un-crosslinked CLCP in 66 parts toluene with 1 part photo-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 the plates. These spacers are such 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 furnace at a temperature of 85°C. 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 (other temperatures such as for example 70°C, or even room temperature for blue material, may be used as an alternative). 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. Other grinding techniques such as ball milling or triple roll milling or ultrasonic agitation may
be used as an alternative.
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, whereas 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 banknotes 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 form 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 form 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 alternative.
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 transmissive 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 d e 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 UV crosslinkable cholesteric liquid crystal polysiloxane polymers have been described in the above embodiments, many other types of CLCP
such as, for example, polyacrylates may be used as an alternative. Specifically the polymers need not be UV 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. Laminae 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 pattern 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 Such 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 through a polarizer. A similar 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 varnish, eye shadow, lipstick etc. UV 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
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 in which the chiral liquid crystal is a chiral liquid crystal polymer.
3. An optical material as claimed in claim 1 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 wherein the laminae are constituted by a layer on particles of a different material.
6. An optical material as claimed in claim 2 in which the laminae comprise a plurality of layers each layer having a different reflection characteristic.
7. An optical material as claimed in claim 2 in which some laminae have different reflection characteristics to others.
8. An optical material as claimed in claim 2 in which the light transmissive medium is coloured.
9. An optical material as claimed in claim 2 in which the laminae are in the form of flakes.
10. A paint, ink, security marking agent, or cosmetic including an optical material as claimed in any preceding claim.
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB9307038 | 1993-04-05 | ||
GB9307038A GB2276883A (en) | 1993-04-05 | 1993-04-05 | Optical material containing a liquid crystal |
PCT/GB1994/000664 WO1994022976A1 (en) | 1993-04-05 | 1994-03-30 | Optical material |
Publications (1)
Publication Number | Publication Date |
---|---|
EP0693098A1 true EP0693098A1 (en) | 1996-01-24 |
Family
ID=10733337
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP94912013A Withdrawn EP0693098A1 (en) | 1993-04-05 | 1994-03-30 | Optical material |
Country Status (4)
Country | Link |
---|---|
EP (1) | EP0693098A1 (en) |
AU (1) | AU6433594A (en) |
GB (1) | GB2276883A (en) |
WO (1) | WO1994022976A1 (en) |
Families Citing this family (35)
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 |
DE4418075C2 (en) * | 1994-05-24 | 2000-06-29 | Daimler Chrysler Ag | Effect lacquer or effect lacquering, in particular for vehicle bodies, using liquid-crystalline interference pigments |
DE4441651A1 (en) * | 1994-11-23 | 1996-04-25 | Basf Ag | Polymerisable material 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 |
EP0880570B1 (en) | 1996-02-15 | 2002-05-22 | MERCK PATENT GmbH | Cholesteric flakes |
FR2750599B1 (en) * | 1996-07-02 | 1998-12-31 | Oreal | NOVEL COSMETIC COMPOSITIONS COMPRISING LIQUID CRYSTAL COLORING AGENTS AND THEIR USE |
DE19715993A1 (en) * | 1997-04-17 | 1998-10-22 | Clariant Gmbh | Polymer laminates with increased hiding power |
KR20010021704A (en) * | 1997-07-09 | 2001-03-15 | 사덱엠 파리스 | Coloring media having improved brightness and color characteristics |
EP0911758B1 (en) * | 1997-07-29 | 2005-11-30 | Nhk Spring Co.Ltd. | Optical identification system using cholesteric liquid crystals |
DE19737618A1 (en) | 1997-08-28 | 1999-03-04 | Consortium Elektrochem Ind | Machine-detectable security marking with increased protection against forgery, production of the security marking and security system comprising this security marking |
DE59807086D1 (en) | 1997-09-02 | 2003-03-06 | Basf Ag | CHOLESTERIC EFFECT LAYERS AND METHOD FOR THE PRODUCTION THEREOF |
JP4465104B2 (en) | 1997-09-02 | 2010-05-19 | ビーエーエスエフ ソシエタス・ヨーロピア | Multilayer cholesteric pigment |
DE19820225A1 (en) * | 1998-05-06 | 1999-11-11 | Basf Ag | Multi-layer cholesteric pigments |
DE19906589A1 (en) * | 1999-02-17 | 2000-08-24 | Basf Ag | Cholesteric laminate material for production of flake pigments and coating materials comprises two cholesteric layers with an interlayer of adhesive material |
US6359056B1 (en) | 2000-01-27 | 2002-03-19 | Kodak Polychrome Graphics Llc | Printing plate and method to prepare a printing plate |
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 |
US7033653B2 (en) | 2001-04-24 | 2006-04-25 | Merck Patent Gmbh | Birefringent marking |
US7081282B2 (en) | 2001-07-02 | 2006-07-25 | Merck Patent Gmbh | Optically variable marking |
AU2003242639A1 (en) | 2002-07-06 | 2004-01-23 | Merck Patent Gmbh | Flakes comprising non-chiral liquid crystal material |
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 |
US6829075B1 (en) * | 2003-05-20 | 2004-12-07 | 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 |
DE102004039355A1 (en) * | 2004-08-12 | 2006-02-23 | Giesecke & Devrient Gmbh | Security element and method for its production |
DE102004021246A1 (en) | 2004-04-30 | 2005-11-24 | Giesecke & Devrient Gmbh | Security element and method for its production |
DE102004021247A1 (en) | 2004-04-30 | 2005-11-24 | Giesecke & Devrient Gmbh | Security element and method for its production |
CN1997940B (en) * | 2004-07-13 | 2011-12-14 | 斯蒂茨丁荷兰聚合物学会 | Microstructuring method of mesogens using contact printing |
CA2537732A1 (en) * | 2005-04-06 | 2006-10-06 | Jds Uniphase Corporation | High chroma optically variable colour-shifting glitter |
AU2006249295A1 (en) | 2005-12-15 | 2007-07-05 | Jds Uniphase Corporation | Security device with metameric features using diffractive pigment flakes |
DE102006015023A1 (en) | 2006-03-31 | 2007-10-04 | Giesecke & Devrient Gmbh | Security element for security papers, value documents, has relief structure, which is formed on basis of cholesteric, liquid crystalline polymer material and top layer contains reflecting or high-refracting layer |
EP1876216A1 (en) | 2006-06-27 | 2008-01-09 | Sicpa Holding S.A. | Cholesteric multi-layers |
MX2010003706A (en) | 2007-10-09 | 2010-04-21 | Sicpa Holding Sa | Security marking authentication device. |
FR2932070B1 (en) | 2008-06-10 | 2012-08-17 | Oreal | MAKE-UP AND / OR CARE OF LASHES |
FR2939033B1 (en) | 2008-12-02 | 2012-08-31 | Oreal | COSMETIC COMPOSITION FOR MAKE-UP AND / OR CARE OF KERATINIC MATERIALS, AND METHOD FOR MAKE-UP |
FR2953715B1 (en) | 2009-12-11 | 2012-02-17 | Oreal | ANHYDROUS FLUID FILTERING COMPOSITION COMPRISING AN OILY PHASE, A PARTICULAR TRIAZINE FILTER AND A RHEOLOGICAL AGENT THAT IS THICKENING OR GELIFYING OIL |
US9778201B2 (en) | 2012-07-03 | 2017-10-03 | Sicpa Holding Sa | Capsule or cork comprising security features |
JP7022151B2 (en) * | 2017-12-28 | 2022-02-17 | 富士フイルム株式会社 | Laminated body, manufacturing method of laminated body and image display device |
Family Cites Families (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB8820100D0 (en) * | 1988-08-24 | 1988-09-28 | Willmore P J | Decoration of substrates |
ATE89306T1 (en) * | 1988-09-09 | 1993-05-15 | Akzo Nv | THERMOCHROMIC COATING. |
ATE112586T1 (en) * | 1989-02-13 | 1994-10-15 | Akzo Nobel Nv | LIQUID CRYSTAL PIGMENT, METHOD OF MANUFACTURE AND USE IN CLOTHING. |
DE3942663A1 (en) * | 1989-12-22 | 1991-06-27 | Gao Ges Automation Org | DATA CARRIER WITH A LIQUID CRYSTAL SECURITY ELEMENT |
GB9004161D0 (en) * | 1990-02-23 | 1990-04-18 | Merck Patent Gmbh | Colourant |
WO1993012195A1 (en) * | 1991-12-09 | 1993-06-24 | MERCK Patent Gesellschaft mit beschränkter Haftung | Thermochromic effect pigment and process for producing the same |
-
1993
- 1993-04-05 GB GB9307038A patent/GB2276883A/en not_active Withdrawn
-
1994
- 1994-03-30 EP EP94912013A patent/EP0693098A1/en not_active Withdrawn
- 1994-03-30 WO PCT/GB1994/000664 patent/WO1994022976A1/en not_active Application Discontinuation
- 1994-03-30 AU AU64335/94A patent/AU6433594A/en not_active Abandoned
Non-Patent Citations (1)
Title |
---|
See references of WO9422976A1 * |
Also Published As
Publication number | Publication date |
---|---|
AU6433594A (en) | 1994-10-24 |
WO1994022976A1 (en) | 1994-10-13 |
GB9307038D0 (en) | 1993-05-26 |
GB2276883A (en) | 1994-10-12 |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
WO1994022976A1 (en) | Optical material | |
EP0720753B1 (en) | Coloured material | |
EP1203968B1 (en) | Production method for an optical laminate | |
JP3670963B2 (en) | Liquid crystalline film | |
EP2749430A1 (en) | Authentication medium | |
JP2002040252A (en) | Optical sheet containing cholesteric liquid crystal layer, information recording body using the same, method for recording information and method for discriminating information | |
EP4040201A1 (en) | Display medium, display product, and display set | |
WO2017110225A1 (en) | Optical film | |
WO2005002874A1 (en) | Structure for identifying object and object provided with that structure | |
US20100046071A1 (en) | Latent image forming film, latent image identifying kit and method for identifying latent image | |
WO2018008231A1 (en) | Optical film and method for producing optical film | |
WO2017191755A1 (en) | Optical film and method for manufacturing optical film | |
JP4286377B2 (en) | Method for producing cholesteric liquid crystal film | |
JP2001004835A (en) | Manufacture of polaliz diffraction element | |
JP4674829B2 (en) | Optical laminate | |
JP4674830B2 (en) | Optical laminate | |
EP1132450A2 (en) | Multilayer reflective film or pigment with viewing angle dependent reflection characteristics | |
JP4309514B2 (en) | Polarization diffraction element | |
JP2001004834A (en) | Polarizing diffraction element | |
JP4286384B2 (en) | Method for manufacturing polarization diffraction element | |
JP2000347030A (en) | Manufacture of cholesteric liquid crystalline film | |
GB2282146A (en) | Chiral liquid crystal lamina with distinct regions | |
JP2001004832A (en) | Cholesteric liquid crystal film | |
JP2001004830A (en) | Cholesteric liquid crystal film | |
JP2001004831A (en) | Cholesteric liquid crystal film |
Legal Events
Date | Code | Title | Description |
---|---|---|---|
PUAI | Public reference made under article 153(3) epc to a published international application that has entered the european phase |
Free format text: ORIGINAL CODE: 0009012 |
|
17P | Request for examination filed |
Effective date: 19950914 |
|
AK | Designated contracting states |
Kind code of ref document: A1 Designated state(s): CH DE FR GB LI |
|
STAA | Information on the status of an ep patent application or granted ep patent |
Free format text: STATUS: THE APPLICATION IS DEEMED TO BE WITHDRAWN |
|
17Q | First examination report despatched |
Effective date: 19970321 |
|
18D | Application deemed to be withdrawn |
Effective date: 19961001 |