HK1116213B - Cholesteric monolayers and monolayer pigments with particular properties, their production and use - Google Patents

Description

Cholesteric monolayers and monolayer pigments with specific properties, their production and use

The present invention provides novel cholesteric monolayers and pigments obtained therefrom which have a high brilliance and a viewing angle-dependent color change (color-flop/tilt effect) and additionally specific properties such as magnetizability, conductivity, fluorescence, phosphorescence and increased hiding power, a process for their production and their use.

Materials having a Liquid Crystal (LC) structure and a chiral phase (LC materials), also called cholesteric LC, are known. The production of such materials from LC organosiloxanes is described, for example, in patent US5,211,877. Pigments having an oriented three-dimensional cross-linked substance (LC pigments) having a liquid crystal structure and a chiral phase are also industrially produced and used. This is described, for example, in German laid-open specification DE 4240743A 1 and patent US5,362,315.

Cholesteric LC layers are preferably highly transparent and reflect light or allow it to pass through. These layers are characterized by selective color reflection as a function of viewing angle (color-flop/tilt effect), also known as optical variability. Absorption does not occur in the LC layer. Cholesteric layers or pigments produced therefrom by comminution therefore do not have any hiding power and, to produce color, must be applied to a dark background, ideally a black background, so that the light fractions transmitted by them are absorbed by the background and their reflected color can be seen depending on the viewing angle. Alternatively, they may be formulated with absorbing pigments, such as carbon black. A significant disadvantage of this method is that part of their color effect is eliminated, since the opaque pigment covers some LC pigment platelets, which can no longer contribute to reflection and thus to the color effect.

When additional properties, such as conductivity, magnetism, altered color (coloristic properties) or hiding power, are to be introduced into these LC layers, the difficulty is that when absorbers or opaque or other non-liquid-crystalline materials are added to cholesteric LC mixtures, their orientation is impaired, as a result of which the reflection properties and thus the color and brightness are lost or at least greatly reduced. These disadvantages are identified in european patent EP 1009776B 1, since the introduction of foreign pigments into the cholesteric matrix causes a considerable part of the reflection wavelength of the LC pigment to be absorbed or scattered, so that the particular advantages of cholesteric interference pigments are substantially eliminated.

A further problem disclosed by european patent EP 1009776B 1 is that a good fine dispersion of the foreign pigments in the cholesteric matrix is required. This dispersion can be carried out only in combination with additives adjusted to the pigment surface, for example fatty acids or lecithin, although it interrupts the formation of helical orientation and thus optimum color development. Thus, cholesteric interference pigments are obtained which give the impression of unattractive colour and have a low colour-flop/tilt effect.

European pending publications EP 0601483A 1 and EP 0686674A 1 describe the incorporation of carbon black or pigments into cholesteric matrices. Possible solutions to this problem are given in patents EP 1017755B 1, EP 1009776B 1 and DE 19619973 a1, for example in order to obtain better hiding power in cholesteric LC layers or LC pigments obtained therefrom. Producing a multilayer product. This consists of a sandwich of two outer oriented polymerized cholesteric LC layers and an intermediate non-liquid crystalline, partially or completely light absorbing layer comprising, for example, carbon black as an absorbing additive. According to European patent EP 1017755B 1, the absorption additive may additionally also have magnetic properties. EP 1017755B 1 thus specifically rejects the possibility of introducing any kind of particles into a single cholesteric LC layer; it is instead proposed to provide a further separate layer with such particles.

When LC pigments are obtained from multilayer films, for example in DE 19820225 a1, their hiding power is less affected by the background and a bright and color-changing surface is displayed regardless of which side is on the background. A disadvantage of these methods for solutions is that these laminates can only be obtained by complex and multistage processes. In addition, the pigment obtained by pulverizing this laminate has a high thickness. Therefore, they do not meet the usual thickness requirements for pigments for coatings and printing inks, since for many coating and printing techniques the range of application of platelet-shaped pigments generally increases with thinner layer thicknesses of the platelets. Furthermore, as described in german laid-open specification DE 19820225 a1, there is a risk of delamination of the absorber layer from the LC layer in multilayer cholesteric pigments.

It is therefore an object of the present invention to provide three-dimensionally crosslinked cholesteric monolayers and cholesteric pigments obtained therefrom which exhibit high brilliance, colour reflectance and colour-flop/tilt effects and which have additional properties, such as increased hiding power, conductivity, luminescence, fluorescence, phosphorescence, colour properties which are changed compared to the initial LC mixture without additives or magnetism, without the necessity of additionally adding layers of additional materials comprising these additional properties.

It has surprisingly been found that, contrary to the prior art, the underlying object of the present invention is achieved by the direct incorporation of nanoparticles with further properties into cholesteric matrices, as a result of which LC layers and LC pigments with increased hiding power and/or other properties, such as magnetic properties, can be provided without leading to the disadvantages detailed above.

The present invention thus provides cholesteric liquid crystal monolayers and monolayer pigments comprising nanoparticles. These layers and pigments are preferably prepared by mixing the nanoparticles into the cholesteric liquid-crystal mixture at a temperature above the clearing point of the cholesteric liquid-crystal mixture.

Nanoparticles are understood according to the invention to mean particles having a particle size in the nanometer range, i.e. 1 to 999nm, preferably 10 to 500 nm.

According to the present invention a monolayer is to be understood to mean a single layer which is not in contact with other layers comprising cholesteric liquid crystal material. The monolayer pigments according to the present invention comprise a single layer with three-dimensionally crosslinked cholesteric liquid-crystal mixtures and nanoparticles.

The cholesteric liquid-crystal mixtures of the invention preferably comprise:

A) 0.01 to 50 wt.%, preferably 0.1 to 10 wt.%, based on the total solids content, of nanoparticles selected from the group consisting of metal oxides, iron oxides, magnetic powders, zinc oxide, carbon black, graphite, fumed silica, luminescent pigments, fluorescent pigments, phosphorescent pigments, metals, metal alloys and color pigments or mixtures thereof,

B) from 20 to 99.5% by weight, preferably from 60 to 99% by weight, based on the total solids content, of at least one or more than one three-dimensionally crosslinkable compound of the average general formula (1),

y¹-A¹-M¹-A²-y² (1)

wherein

Y¹、Y²Identical or different and are each a polymerizable group, for example an acrylate or methacrylate group, an epoxy group, an isocyanate, a hydroxyl group, a vinyl ether or a vinyl ester group,

A¹、A²is of the formula C_nH_2nWherein n is an integer of 0 to 20 and one or more methylene groups may be replaced by oxygen atoms, and

M¹having the formula-R¹-X¹-R²-X²-R³-X³-R⁴-，

R¹、R²、R³，R⁴Are identical or different divalent radicals selected from the group consisting of-I-, -COO-, -CONH-, -CO-, -S-, -C.ident.C-, -CH-, -N-, -N-N (O) -or a C-C bond, and R is a divalent radical of a group²-X²-R³Or R²-X²Or R²-X²-R³-X³It may also be a C-C bond,

X¹、X²、X³are identical or different radicals selected from: 1, 4-phenylene, 1, 4-cyclohexylene, B having 6 to 10 atoms in the aryl ring¹、B²-and/or B³Substituted arylene or heteroarylene radicals, which may contain 1 to 3 heteroatoms from the group O, N and S, or B having 3 to 10 carbon atoms¹-、B²-and/or B³-a substituted cyclohexylene group, and

B¹、B²、B³are identical or different substituents selected from the group consisting of: hydrogen, C₁-C₂₀Alkyl radical, C₁-C₂₀-alkoxy, C₁-C₂₀Alkylthio radical, C₂-C₂₀-alkylcarbonyl group, C₁-C₂₀Alkoxycarbonyl, C₁-C₂₀-alkylthio carbonyl, -OH, -F, -Cl, -Br, -I, -CN, -NO₂Formyl, acetyl and alkyl, alkoxy or alkylthio groups each interrupted by an ether oxygen, a thioether sulfur or an ester group and having 1 to 20 carbon atoms,

C) from 0.5 to 80% by weight, preferably from 3 to 40% by weight, based on the total solids content, of at least one or more than one chiral compound of the average general formula (2),

V¹-A¹-W¹-Z-W-A²-V² (2)

wherein

V¹、V²Identical or different and are each an acrylate or methacrylate group, an epoxy group, a vinyl ether or vinyl ester group, an isocyanate group, C₁-C₂₀Alkyl radical, C₁-C₂₀-alkoxy, C₁-C₂₀Alkylthio radical, C₁-C₂₀Alkoxycarbonyl, C₁-C₂₀-alkylthio carbonyl, -OH, -F, -Cl, -Br, -I, -CN, -NO₂Formyl, acetyl and alkyl, alkoxy or alkylthio groups each interrupted by an ether oxygen, a thioether sulfur or an ester group and having 1 to 20 carbon atoms, or a cholesterol group,

A¹、A²each as defined above, is capable of,

W¹、W²each having the formula-R¹-X¹-R²-X²-R³-，

R¹、R²、R³Each as defined above and R²Or R²-X²Or X¹-R²-X²-R³It may also be a C-C bond,

X¹、X²each as defined above and

z is a divalent chiral group selected from dianhydrohexitol, hexose, pentose, binaphthyl derivatives, biphenyl derivatives, tartaric acid derivatives or optically active diols, andat V¹Or V²In the case of a cholesterol group, this is a C-C bond.

According to the invention, all conventional nanoparticles in the sense defined in the present invention can be used. Such nanoparticles are commercially available or can be produced in the usual manner known to the person skilled in the art, for example by comminuting larger particles, for example by grinding processes, or advantageously by direct synthesis under controlled conditions from soluble or gaseous precursors (colloidal techniques). According to the invention, the nanoparticles have additional properties, such as increased hiding power, conductivity, luminescence, fluorescence, phosphorescence or magnetism. These additional properties may be used, for example, as additional security features.

The magnetic nanoparticles may be selected, for example, from ferromagnetic elements, such as iron, cobalt, nickel or alloys or mixed oxides thereof, such as ferrite M^IIO×Fe₂O₃Wherein the divalent metal M used is, for example, zinc, cadmium, cobalt, manganese, copper or magnesium. Using iron as the divalent metal, the result being, for example, magnetite Fe₃O₄. Particular preference is given to using gamma-Fe₂O₃Or CrO₂As magnetic nanoparticles. In addition, the magnetic nanoparticles may also include, for example, an aluminum-nickel-cobalt alloy having a main component such as iron, cobalt, nickel, copper, or titanium. In the context of the present invention, luminescence, as a generic term, includes fluorescence and phosphorescence, which differ significantly in the decay time of the persistent luminescence. Luminescent nanoparticles may consist of, for example, organic fluorescent pigments such as bis (azomethine) pigments or inorganic materials such as apatite, fluorite, calcite, corundum, etc. The phosphors may be of natural (fluorite, etc.) or synthetic (zinc sulfide, etc.) origin, and the emission may originate from any type of light emitting site (main, transition, or rare earth atoms, ions or atomic groups, etc.).

Cholesteric liquid crystal monolayers and monolayer pigments comprising nanoparticles have surprising advantages over european pending publications EP 0601483 a1 and EP 0686674 a1 in which the incorporation of carbon black or pigments into cholesteric matrices is described: the use of nanoparticles as additives provides a significantly brighter and more attractive color reflection of the cholesteric layer obtained or of the pigment obtained therefrom.

In a further preferred embodiment, organic nanoparticles having absorbing properties, such as azo pigments, metal complex pigments, such as azo and azomethine metal complexes, isoindolinone and isoindoline pigments, phthalocyanine pigments, quinacridone pigments, perinone and perylene pigments, anthraquinone pigments, diketopyrrolopyrrole pigments, thioindigo pigments, bisdiketopyrrolopyrrole pigments, perylene pigments, and the likeOxazine pigments, triphenylmethane pigments, and quinophthalone pigments.

Suitable nanoparticles having the properties of a colour, black or white pigment according to the invention are, for example, metal oxides such as TiO₂、ZrO₂、Al₂O₃、ZnO、SnO₂Iron oxides, including in particular black magnetite (Fe)₃O₄) Chromate, vanadate and sulfide, a wide variety of carbon black types, in particular easily dispersible pigment black, graphite pigments and over-dyed white pigment particles.

In a preferred embodiment, the nanoparticles are not treated on the surface, for example with additives adjusted to the pigment surface, such as fatty acids or lecithin, but it surprisingly does not lead to the described disadvantages of the prior art in unsatisfactory dispersed form.

In further embodiments, the nanoparticles used may be fumed silica in their various particle sizes and embodiments, for example, as hydrophilic or hydrophobic variations.

Particularly preferred liquid-crystalline mixtures are based on the use of crosslinkable organosiloxanes or on substances having a thermotropic twisted nematic, smectic, discotic or lyotropic phase.

The present invention provides crosslinked liquid crystal monolayers, preferably with a film thickness of 0.5-50 μm, obtainable by polymerizing a three-dimensionally crosslinked cholesteric liquid-crystal mixture comprising nanoparticles.

The invention further provides a process for producing a liquid-crystal monolayer, characterized in that a three-dimensionally crosslinked cholesteric liquid-crystal mixture comprising nanoparticles is used to obtain a film, preferably having a thickness of 0.5 to 50 μm, on a support, and the three-dimensional polymerization of the liquid-crystal film is carried out, for example, by electron beam curing, ultrasonic polymerization or UV polymerization.

The three-dimensionally crosslinked cholesteric liquid-crystal mixtures comprising nanoparticles are preferably obtained by mixing the nanoparticles into the three-dimensionally crosslinked cholesteric liquid-crystal mixture at a temperature above the clearing point by methods known from the prior art, such as Dispermats, extruders, roll mills, static mixers and dissolvers.

The polymerization is preferably carried out by UV crosslinking, wherein from 0.1 to 3% by weight, preferably from 0.5 to 1.5% by weight, of a photoinitiator is added to the three-dimensionally crosslinked cholesteric liquid-crystal mixtures according to the invention. If appropriate, stabilizers may also be added in amounts of from 50 to 3000ppm, preferably 200 and 1000ppm, to prevent premature and uncontrolled polymerization.

Preferably, a 1-5 μm thick film is obtained on a support, such as a PET film. This is preferably carried out by roll coating or knife coating at a belt speed of from 1 to 200 m/min. The film formation is more preferably carried out at 20 to 80 m/min. Further preferred embodiments employ a laminated film, for example made of PET, or under inert conditions, for example in N₂Working under an atmosphere.

Thus, cholesteric liquid-crystal monolayers according to the invention with high brightness and color reflection capability and flip-flop/tilt effects are obtained, which can be used as security markings.

The monolayers of the invention are preferably used, for example, as components of laminates as security strips or in the form of film elements similar to holograms or activity images on banknotes or certificates or other documents of value.

These monolayers can be further processed by the process according to the invention to give cholesteric liquid-crystal monolayer pigments. For this purpose, the monolayer is removed from the support by means of a suitable erosion unit, for example a stripping unit or stripping blade, to form a coarse liquid-crystal flake, which is comminuted with a suitable tool, for example a milling or cutting unit, to give the liquid-crystal pigment and optionally classified by sieving and sifting. The pigments prepared according to the invention preferably have a thickness of from 0.1 to 50 μm and a diameter of from 10 to 1000. mu.m. They are more preferably 0.5 to 6 μm thick and 1 to 200 μm in diameter.

A further preferred embodiment for the production of liquid crystal monolayers and pigments is carried out from organic solutions of the LC mixture components with suitably dispersed nanoparticles. In this case, solution coating, which involves initial evaporation of the solvent after wet film coating and before polymerization, is performed while maintaining other boundary conditions. The advantage of this variant lies in simpler dispersion, for example by ultrasound of the additives in solution.

The liquid-crystal pigments of the invention thus obtained can be used for printing products, for the production of paints and inks, for the colouring of plastics and for the production of magnetic strips. They have the advantage that they can be produced with very low thicknesses while maintaining the desired properties and can therefore be used in a very wide range of applications.

The pigments of the invention, for example formulated as printing inks, can be used for printable optical features, for example on the mentioned valuable documents, with the advantage that further features are integrated in addition to the non-reproducible color-tilt effect. This feature may be designed as an overt or covert feature.

The present invention further provides the use of the liquid crystal pigments of the invention comprising nanoparticles having magnetic properties for the production of structured, printed, optically variable security features, wherein a further alignment pattern is obtained by applying an external magnetic field during the curing phase of a printing ink comprising magnetic nanoparticles comprising the liquid crystal pigments of the invention. In a preferred embodiment, in the case of the magnetic cholesteric LC pigments according to the invention, a magnetic field is therefore applied directly to the printed substrate after the printing of the corresponding printing ink onto the preferably dark background, before the binder is cured, so that the alignment pattern of the magnetic LC pigments in the printed features is obtained according to the selected magnetic field geometry, since the platelet-shaped magnetic pigments are aligned along the field lines. A key factor in this process is the correct adjustment of the viscosity of the base stock. When the printed pattern treated in this way is subsequently cured under the effect of this external magnetic field, an optically variable feature is obtained which, in addition to the color-hopping human identification feature and the known circular polarization effect of the reflected light from the cholesteric material, has permanent information in the form of a pigment alignment pattern. In this way, a separate personalization measure of the optically variable security feature is provided. This further personalized pattern has the advantage that it increases the security against counterfeiting. Depending on the design, such individual patterns as distinct features can even be recognized by laymen without further aid and can be used to distinguish originals from artifacts. The printing ink base used in such a process can have a solvent-based formulation or a water-based formulation or be designed as a UV-curing system.

Possible printing methods that may be considered as an option for the cholesteric liquid crystal pigments of the invention include processes selected from: screen printing, flexography and gravure printing, but also selected from, for example, offset and gravure printing or pad printing.

Furthermore, the liquid-crystalline pigments according to the invention can also be used in coatings for industrial or automotive applications. Further possible uses of the liquid-crystal pigments according to the invention are the coloration of plastics by masterbatches or compounding, and the use as writable and readable variable-colour magnetic strips.

The invention is illustrated in detail below with reference to non-limiting examples.

Examples

Example 1: preparation of the chiral Compound bis-2, 5- [4- (Acryloyloxy) benzoyl ] isosorbide

20.0g of isosorbide (137mmol) and 73.2g of triethylamine (723mmol) are dissolved in 120ml of toluene. A solution of 60.5g (287mmol)4- (acryloyloxy) benzoyl chloride (prepared according to Lorkowski, H.J.; Reuther, F.Acta Chim.Acad.Sci.Hung.1977, 95, 423-34) was added dropwise to 60ml toluene at 80 ℃. The mixture was stirred at 80 ℃ for 2h and then mixed at room temperature with 80ml of 10% hydrochloric acid, the organic phase was washed with water (2X 80ml) and 10% sodium bicarbonate solution (80ml) and dried over sodium sulfate, and the solvent was removed under reduced pressure to a toluene content of about 20% by weight. The syrup obtained was mixed with 220ml ethanol and 200ml cyclohexane and heated to 80 ℃ with stirring. After cooling and filtration, bis-2, 5- [4- (acryloyloxy) benzoyl ] isosorbide having a melting point of 115 ℃ is obtained in a yield of 45.9g (68% of theory).

Example 2: green liquid crystal mixture

93g of hydroquinone bis [4- (4-acryloylbutoxy) benzoate](available from Broer, D.J.; MoI, G.N.; Challa, G.Makromol. chem.1991, 192, 59), 7g2, 5-bis [4- (acryloyloxy) benzoyl ] carbonyl]Isosorbide (obtainable according to example 1), 1.00g Irgacure819 photoinitiator and 0.20g 2, 6-di-tert-butyl-4-dimethylaminomethylene) phenol (Ethanox)703 Ethyl corp, Baton Rouge, LA 70801) were weighed in. The mixture was homogenized at the oil bath temperature of 150 ℃ by means of a precision glass stirrer until a clear melt was obtained. The clear point of the mixture was 146 ℃ and the viscosity at 100 ℃ was about 200 mPas. A film of this mixture, which had a bright green color when viewed on a black background, turned blue when the viewing angle was increased, was produced between two microscope slides by shearing at 110 ℃ and crosslinked under a UV laboratory lamp. The reflection maximum (Perkin-Elmer Lambda 18UV/VIS spectrometer) of this film at 0 °/6 ° is 516 nm.

Example 3: production of the Green liquid Crystal mixtures of the invention Using dispersed magnetic powders

1.5kg of the green liquid-crystal mixture obtainable according to example 2 were melted at 130 ℃ in a drying cabinet and 75g of a black magnetic powder MR 210(200nm, MR-Chemie GmbH, D-59427 Unna) were subsequently dispersed therein at 110 ℃ in a laboratory dissolver (from PC Labosystem, Switzerland) at a maximum shear rate for 40 min. A film of this mixture, which when viewed on a black background has a bright metallic green color that changes to blue when the viewing angle is increased, is produced between two microscope slides by shearing at 110 ℃ and is crosslinked under a UV lamp. The viewing angle-dependent color change is clearly visible even on a white background.

Example 4: production of cholesteric LC films of the invention

The green LC mixture with dispersed magnetic powder obtainable according to example 3 was applied as a melt on a PET Film (RNK 19, Mitsubishi Polyester Film, 65023 Wiesbaden) by roll coating at 100 ℃ to obtain a Film with a thickness of about 4 μm and laminated with a second PET Film for better orientation and to prevent oxygen inhibition of the LC molecules. The laminated LC film is then three-dimensionally crosslinked under UV light on a coater and the laminated film is removed again. The film thus obtained, when a black background is observed underneath, shows a bright metallic green color which, when the film is tilted, changes to a bright blue color. This color change is clearly visible even on a non-absorbing background.

Example 5: production of cholesteric LC pigments of the invention with increased hiding power and magnetic Properties

The LC film with finely dispersed magnetic powder obtainable according to example 4 was removed from the carrier film with an etching system to obtain a coarse foil. The flakes were ground in a laboratory mill and the ground material was sieved through a 40 μm screen. The average platelet diameter of the pigment thus obtainable is about 35 μm. Knife coating 3 wt% of these pigments in a Clear base (e.g., Tinted Clear additive Deltron 941, PPG Industries, UK-Suffolk IP 142 AD) shows a bright metallic green color on a black background that changes to metallic blue when the sample is tilted. The corresponding knife coating of these pigments on a white background showed a weaker but still clear green-blue tilt effect with high gloss compared to a black background. Smaller magnets attract these pigments over a distance of at most 1cm and they collect at the poles of the magnets. Using a dispersion of these magnetic LC pigments in a binder that has not yet solidified, a pattern can be obtained in the petri dish by applying a magnet to the outside of the dish bottom, according to the different alignment/orientation of the pigments in the magnetic field, which is fixed by solidifying the binder.

Example 6: production of cholesteric LC pigments according to the invention with metallic luster

Analogously to example 3, 20g of fumed silica (HDK)H20, Wacker-Chemie GmbH, Munich) was incorporated into 1kg of a green cholesteric LC mixture obtainable according to example 2. From this cholesteric LC mixture, analogously to example 4, a crosslinked cholesteric film is obtained, from which the LC pigments according to the invention can be produced analogously to example 5 using dispersed silica. The average platelet diameter of the pigment thus obtainable is about 35 μm. 2% by weight of these pigments are knife-coated in a Clear base (e.g. Tinted Clear Additive Deltron 941, PPG industries, UK-Suffolk IP 142 AD) showing a bright metallic greenish color on a black background which changes to a metallic bluish hue when the sample is tilted. These inventive pigments exhibit considerably different coloristic properties compared to cholesteric pigments made from the same LC mixture without the addition of fumed silica. They give the impression of a distinctly more metallic and brighter shade in each case at different viewing angles.

Claims (15)

1. Liquid crystal monolayer comprising a three-dimensionally crosslinked cholesteric liquid crystal mixture and nanoparticles, wherein the nanoparticles have a particle size of 1 to 200nm and have magnetic properties.

2. A liquid crystal monolayer according to claim 1 wherein the nanoparticles are selected from magnetic powders.

3. Liquid crystal monolayer according to claim 1, wherein the nanoparticles are selected from ferromagnetic elements or alloys thereof or mixed oxides thereof or aluminium-nickel-cobalt alloys having a main component of iron, cobalt, nickel, copper or titanium, wherein the ferromagnetic elements are selected from iron, cobalt and nickel.

4. A liquid crystal monolayer according to claim 1 wherein the liquid crystal mixture comprises:

A) 0.01 to 50 wt.%, based on the total solids content, of nanoparticles selected from the group consisting of magnetic powders,

B) from 20 to 99.5% by weight, based on the total solids content, of at least one or more than one three-dimensionally crosslinkable compound of the average general formula (1),

Y¹-A¹-M¹-A²-Y² (1)

wherein

Y¹、Y²Identical or different and are each a polymerizable group,

A¹、A²is of the formula C_nH_2nWherein n is an integer of 0 to 20 and one or more methylene groups may be replaced by oxygen atoms, and

M¹having the formula-R¹-X¹-R²-X²-R³-X³-R⁴-，

R¹、R²、R³、R⁴Are identical or different divalent radicals selected from the group consisting of-O-, -COO-, -CONH-, -CO-, -S-, -C.ident.C-, -CH-, -N-, -N-N (O) -or a C-C bond, and R²-X²-R³Or R²-X²Or R²-X²-R³-X³It may also be a C-C bond,

X¹、X²、X³are identical or different radicals selected from: 1, 4-phenylene, 1, 4-cyclohexylene, B having 6 to 10 atoms in the aryl ring¹-、B²-and/or B³Substituted arylene or heteroarylene radicals, which may contain 1 to 3 heteroatoms selected from O, N and S, B having 3 to 10 carbon atoms¹-、B²-and/or B³-a substituted cyclohexylene group, and

B¹、B²、B³are identical or different substituents selected from the group consisting of: hydrogen, C₁-C₂₀Alkyl radical, C₁-C₂₀-alkoxy, C₁-C₂₀Alkylthio radical, C₂-C₂₀-alkylcarbonyl group, C₁-C₂₀Alkoxycarbonyl, C₁-C₂₀-alkylthio carbonyl, -OH, -F, -Cl, -Br, -I, -CN, -NO₂Formyl, acetyl and alkyl, alkoxy or alkylthio groups each interrupted by an ether oxygen, a thioether sulfur or an ester group and having 1 to 20 carbon atoms,

C) 0.5 to 80 wt.%, based on the total solids content, of at least one or more than one chiral compound of the average general formula (2),

V¹-A¹-W¹-Z-W²-A²-V² (2)

wherein

V¹、V²Identical or different and are each an acrylate or methacrylate group, an epoxy group, a vinyl ether or vinyl ester group, an isocyanate group, C₁-C₂₀Alkyl radical, C₁-C₂₀-alkoxy, C₁-C₂₀Alkylthio radical, C₁-C₂₀Alkoxycarbonyl, C₁-C₂₀-alkylthio carbonyl, -OH, -F, -Cl, -Br, -I, -CN, -NO₂Formyl, acetyl and alkyl, alkoxy or alkylthio groups each interrupted by an ether oxygen, a thioether sulfur or an ester group and having 1 to 20 carbon atoms, or a cholesterol group,

A¹、A²each as defined above, is capable of,

W¹、W²each having the formula-R¹-X¹-R²-X²-R³-，

R¹、R²、R³Each as defined above and R²Or R²-X²Or X¹-R²-X²-R³It may also be a C-C bond,

X¹、X²each as defined above and

z is a divalent chiral group selected from dianhydrohexitol, hexose, pentose, binaphthyl derivatives, biphenyl derivatives, tartaric acid derivatives or optically active diols and is at V¹Or V²In the case of a cholesterol group, a C-C bond,

provided that the total amount of all components equals 100%.

5. Liquid crystal monolayer according to claim 4, wherein the nanoparticles are selected from ferromagnetic elements or alloys thereof or mixed oxides thereof or aluminium-nickel-cobalt alloys having a main component of iron, cobalt, nickel, copper or titanium, wherein the ferromagnetic elements are selected from iron, cobalt and nickel.

6. A liquid crystal monolayer according to any one of claims 1 to 5, wherein the monolayer has a film thickness of from 0.5 to 50 μm.

7. Method for producing a liquid crystal monolayer according to any of claims 1-5, wherein a mixture of three-dimensionally crosslinked cholesteric liquid crystals and nanoparticles is used to obtain a film having a thickness of 0.5-50 μm on a support, and wherein the nanoparticles have a particle size of 1-200nm and have magnetic properties, and wherein a three-dimensional polymerization of the liquid crystal film is subsequently carried out.

8. Liquid crystal monolayer pigment comprising a monolayer of cholesteric liquid crystal mixture having three-dimensional cross-linking and nanoparticles, wherein the nanoparticles have a particle size of 1-200nm and have magnetic properties.

9. A liquid-crystalline pigment according to claim 8, wherein the pigment has a thickness of 0.1 to 50 μm and a diameter of 10 to 1000 μm.

10. A liquid crystal pigment according to claim 8 or 9, wherein said pigment comprises nanoparticles having magnetic properties.

11. A process for producing cholesteric liquid crystal monolayer pigments comprising the steps of eroding a monolayer comprising a three-dimensionally crosslinked cholesteric liquid crystal mixture and nanoparticles having a particle size of 1-200nm and magnetic properties, producing coarse liquid crystal pigment flakes, and comminuting these flakes to obtain liquid crystal pigment particles.

12. The method of claim 11, wherein the method further comprises the step of classifying the pigment particles.

13. Use of a liquid crystal monolayer according to any of claims 1 to 5 as a security marking.

14. Use of a liquid-crystal pigment according to any one of claims 8 to 10 for printing products, for the production of paints and inks, for colouring plastics, for the production of magnetic strips and security markings.

15. Use according to claim 14, characterized in that the printed product is a structured, printed, optically variable security feature with an additional alignment pattern, which pattern can be obtained by applying an external magnetic field during the curing phase of a printing ink comprising a liquid crystal pigment according to claim 10.