| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | December 22, 1998 |
| PATENT TITLE |
Interference pigments comprising molecules fixed in a cholesteric configuration, and use thereof |
| PATENT ABSTRACT | The invention relates to interference pigments comprising molecules fixed in a cholesteric configuration, and to the use thereof. The pigments of the invention have a plateletlike structure and a thick ness of from 1 .mu.m to 20 .mu.m. They contain oriented, crosslinked substances with a liquid-crystalline structure having a chiral phase |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | May 1, 1995 |
| PATENT FOREIGN APPLICATION PRIORITY DATA | This data is not available for free |
| PATENT CLAIMS |
What is claimed is: 1. A pigment having a structure which is substantially that of a platelet, a thickness of from 1 .mu.m to 20 .mu.m and a diameter of between 500 .mu.m and 5 .mu.m consisting essentially of oriented three-dimensionally, crosslinked substances of a liquid-crystalline structure having a chiral phase. 2. A pigment as claimed in claim 1, wherein said pigment has a thickness of from 3 .mu.m to 10 .mu.m and a diameter of from 10 .mu.m to 100 .mu.m. 3. A pigment as claimed in claim 1, wherein the oriented three-dimensionally crosslinked substances with a liquid-crystalline structure having a chiral phase comprise organosiloxanes in which the number of polymerizable groups is at least two. 4. A pigment as claimed in claim 3, wherein the oriented three-dimensionally crosslinked substances with a liquid-crystalline structure having a chiral phase comprises at least two organosiloxanes. 5. A composition containing a pigment of claim 1. 6. A pigment as claimed in claim 1, prepared by a orienting three-dimensionally crosslinkable substances of a liquid-crystalline structure having a chiral phase, b optionally, adding other pigments, dyes or mixtures thereof, c three-dimensional crosslinking the substances of (a) and d comminuting to a desired particle size. 7. A data carrier comprising the pigment as claimed in claim 1. |
| PATENT DESCRIPTION |
FIELD OF INVENTION The invention relates to interference pigments comprising molecules fixed in a cholesteric configuration, and to the use thereof. BACKGROUND OF INVENTION In addition to the long-widespread color pigments which absorb a fraction of the incident light and reflect the remainder, there is increasing use of pigments which owe their color to interference effects. These pigments are known as pearl luster pigments and are composed of mica platelets to which thin layers of materials having a different optical density have been applied. So that color effects can be produced in the visible wavelength region, it is necessary to use layer thicknesses in the region of a few hundred nanometers, which must be matched exactly from layer to layer. In Merck Kontakte 1992 (2), p. 23, model calculations are used to demonstrate how the originally sharply defined reflection spectrum of a TiO.sub.2 -mica-TiO.sub.2 system becomes "blurred" over the entire visible wavelength region if the layer thicknesses of the mica substrate, instead of being exactly defined, show a Lorenz distribution. The same publication (FIG. 10, page 20) shows reflection curves of the system at different thicknesses of the TiO.sub.2 layer, the marked effect of the layer thicknesses on the form of the curves (intensity and width of the curves) and on the position in the spectrum of light is very evident, and results in very different color effects. The same publication (FIG. 11, page 20) shows the set of reflection curves for a selected TiO.sub.2 -mica-TiO.sub.2 system at different viewing angles (angle of illumination corresponds to viewing angle), owing to the laws of refraction which arise in the case of interference phenomena with light, the curves with a relatively flat viewing angle are displaced toward shorter-wave regions of the spectrum, although all of the reflection curves overlap to a considerable extent. In these model calculations it is necessary to take account of higher-order interference curves, so that a given layer system possesses two or more reflection maxima which may be situated in the visible region and which contribute to the overall color impression. For these reasons a layer system of this kind is not ideally colorless but is milky-white, and at different viewing angles (angle of illumination corresponds to viewing angle, "gloss or reflection condition") no definite change in color can be observed, owing to the overlapping of the wide reflection curves. If, in contrast, the system is viewed at an angle which deviates greatly from the angle of illumination (angular region far outside the "gloss condition"), then in this geometry ("in transmission") the complementary fraction of the light spectrum can be seen. The application of two or more layers of materials with different refractive indices to a substrate enables higher reflection intensities with narrower curves to be obtained, as shown in FIG. 15 (page 21 of the above publication). However, even in this example, only a small region of the red light spectrum, from about 610 nm to 650 nm, occurs without reflection components in the reflection spectrum. A common feature of all of these model calculations is that they start from defined layer thicknesses which extend homogeneously over the entire pigment. The consequence of this for production processes is a need to maintain precise conditions. In EP-A-0 342 533, for example, interference pigments of this kind are prepared by applying metal oxide layers to natural mica platelets which are immersed in an aqueous solution of metal compounds and then dried at temperatures of from 80.degree. C. to 130.degree. C. In contrast, DE-A-42 17 511 describes a process in the gas phase, wherein metal compounds are applied by vapor in a fluidized-bed reactor. In both cases, the individual layers are subject to variations in thickness which lead to the color variations discussed. In WO 93/08237 the fluctuation in thickness which is unavoidable in the case of natural mica is countered by a process which leads to better-defined SiO.sub.2 layers by forming a thin silicate film as precursor material and then drying it. However, this process also has the disadvantage that it is necessary subsequently to coat this carrier substrate with compounds in layer thicknesses which must be maintained precisely, by a set-chemical method or by methods as described in the above-discussed EP-A-0 342 533. Thus in this example, it is not always possible to bring about a precisely defined ratio of layer thickness of substrate layers to metal (oxide) layer(s). Furthermore, the metal compounds which are required in the precursor step for the preparation of conventional interference pigments are frequently toxic and give rise to problems of workplace safety. As Is known from H. -J. Eberle, A. Miller and F. -H. Kreuzer, Liquid Crystals, 1989 (5), 907-916 it is possible to produce novel color effects using liquid-crystalline materials whose molecules are arranged in layers which are twisted with respect to one another (cholesteric liquid crystals with a helical structure): interference effects with light mean that a very narrow range of the beam of light which is incident in a broad spectral region is reflected, whereas all wavelengths lying outside this range are transmitted. In this context, the range of the reflected spectral component is predetermined by the pitch of the helix and the mean refractive index of the material. The half width of the reflection curve is dependent on the molecular refractive-index anisotropy. In addition, the reflected spectral region is divided into a left-handed-and a right-handed-helically polarized light component, one which reflects and the other transmits depending on the twist sense of the helix. As shown for interference pigments, in the case of cholesteric liquid crystals the position of the reflection spectrum is shifted in analogy to Bragg's Law toward the short-wave region when illumination and observation are carried out at flatter angles. In contrast to the interference pigments described, in the case of cholesteric liquid crystals based on organopolysiloxanes, which, as shown in Eberle et al., have been applied as a film to substrate materials, reflection curves of high intensity with narrow half widths can be obtained. In this case, reflection components are absent from broad regions of the spectrum, including the visible region, so that outside the reflection curves of the liquid crystals a baseline prevails with no reflection components. Since in the region of reflection it is only the left-handed-helically polarized light components which are reflected, while the right-handed-helically polarized components as well as the rest of the light spectrum are completely transmitted, these cholesteric materials are transparent over the entire spectral range. Because of the narrow half widths of the reflection curves in systems of this kind it is possible to achieve high brilliance and good color saturation, even under unfavorable light conditions, owing to the marked rise of the reflection curves from the background. Since these curves overlap at different viewing angles under gloss angle conditions either not at all or only in small fractions (FIG. 5a in Eberle et al.), other spectral regions are overlapped by the reflection curve even in the case of relatively small changes in angle, which regions do not include the original regions; in the spectral region in which the "old" reflection curve had its wavelength maximum, the "new" reflection curve goes right back to the baseline. This results in a marked color perception which changes continuously with the viewing angle ("continuous color flop") and differs fundamentally from the above-discussed color flop of conventional interference pigments based on the reflection/transmission condition. If the cholesteric organosiloxanes are applied to colored substrates, it is possible to obtain a great diversity of color effects, whereas a black substrate absorbs completely the light component which is transmitted by the cholesterically configured molecules, with a white substrate the effect is the opposite, the spectrally and spatially diffuse light component of the white substrate competes with the directed spectral component of the cholesteric phase. When colored substrates are used the absorption spectra overlap accordingly with the reflection spectra of the helical structures, which may lead to angle-dependent blue shifts and even inverse red shifts at relatively flat viewing angles, as Eberle et al., showed using different examples in FIG. 9, Thus, it is possible with red liquid-crystalline material on a dark blue substrate to obtain an angle-dependent color shift which is opposite to that for a green substrate. With an almost perpendicular angle of illumination/viewing angle this leads on the blue substrate to a violet signal and on the green substrate to an orange-colored signal. In contrast, at flatter angles of illumination/viewing the color impression on the green substrate shifts to the green region, corresponding to a shift into the short-wave region of the spectrum. On the blue substrates a turquoise color is formed from the blue absorption color and the green color of the liquid-crystalline material, corresponding to a shift into the long-wave spectral region in relation to the violet color. When red liquid-crystal materials are used on a red substrate, an intensification of color occurs at specific, virtually perpendicular viewing angles, whereas at flatter angles the color flop of the liquid crystal leads to a green color effect which is superimposed on the angle-independent, red absorption color of the substrate and therefore gives an orange color impression. Since the reflection curves of the liquid-crystalline organosiloxanes are on the baseline in broad regions of the visible light spectrum, these regions are "free" for other chromophoric media (pigments, colorants), thus enabling very diverse combinations which may lead to flop intensities and color effects which are always novel. In this context it is irrelevant whether pigments are additionally incorporated into the liquid-crystalline composition or whether a colored substrate is chosen, as is shown for the yellow cholesteric organosiloxane material in FIG. 9 (Eberle et al.,) by way of example. A common factor with all these applications is that the color effect which can be observed in the case of the cholesteric organosiloxanes is only possible within temperature ranges in which the molecules are arranged in helical layers. This temperature range is predetermined by the material. If the material is heated at temperatures situated above this phase range, then the ordered structure becomes disordered, with the result that the constructive interference effects with light which are described are no longer possible; the originally colored material becomes colorless. U.S. Pat. No. 5,211,877 describes materials which retain the characteristic optical properties even outside the liquid-crystalline phase region, following the formation of helically twisted layers these molecules are fixed with the aid of a chemical polymerization reaction, so that these layers are maintained even in temperature ranges outside the liquid-crystalline phase. However, this method requires a planar substrate on which the base layer for the helical structure is able to form; consequently, only planar surfaces can be given color effects of this kind. SUMMARY OF INVENTION The object of the present invention was to provide materials which give brilliant color impressions, changing continuously with the viewing angle, if desired additionally in the UV and IR region, and which can be employed universally with conventional methods of application. The present invention relates to pigments of platelet like structure having a thickness of from 1 .mu.m to 20 .mu.m comprising oriented crosslinked substances with a liquid-crystalline structure having a chiral phase. The pigments according to the invention possess the optical properties of the liquid-crystalline phase (angle-dependent, continuously changing color effect, high brilliance and polarization of reflected light component). Incorporated into conventional binder systems, they can be applied to any desired surfaces, including nonplanar surfaces. Pigments comprising oriented, three-dimensionally crosslinked substances with a liquid-crystalline structure having a chiral phase can be incorporated, individually or in any desired mixture, into a wide range of media using conventional, established process steps. Examples of such media are waterborne coating materials in the form of aqueous dispersions, such as PMA (polymethacrylate), SA (styreneacrylate), polyvinyl derivatives, PVC (polyvinylchloride), polyvinylidene chloride, SB copolymers (impact resistant polystyrine), PV-AC (polyvinyl acetate) copolymer resins, or in the form of water-soluble binders, such as shellac, maleic resins, rosin-modified phenolic resins, linear and branched saturated polyesters, amino resin-crosslinking saturated polyesters, fatty acid-modified alkyd resins, plasticized urea resins, or in the form of water-thinnable binders such as PU (polyurethane) dispersions, EP (epoxy) resins, urea resins, melamine resins, phenolic resins, alkyd resins, alkyd resin emulsions, silicone resin emulsions, and also powder coatings, for example, for triboelectric spraying, such as polyester powder coating resins, PU powder coating resins, EP powder coating resins, EP/SP (epoxy-polyester) hydrid powder coating resins, PMA powder coating resins or powder coatings for fluidized-bed sintering, such as thermoplasticized EPS (extruded polystyrene), LDPE (low density polyethylene), LLDPE (linear low density polyethylene), HDPE (high density polyethylene), and solvent-containing coating materials, for example as one-component and two-component (two-pack) coating materials (binders) such as shellac, rosin esters, maleic resins, nitrocelluloses, rosin-modified phenolic resins, physically drying saturated polyesters, amino resin-crosslinking saturated polyesters, isocyanate-crosslinking saturated polyesters, autocrosslinking saturated polyesters, alkyds with saturated fatty acids, linseed oil alkyd resins, soya oil resins, sunflower oil alkyd resins, safflower oil alkyd resins, ricinenic alkyd resins, wood oil/linseed oil alkyd resins, mixed oil alkyd resins, resin-modified alkyd resins, styrene/vinyltoluene-modified alkyd resins, acrylicized alkyd resins, urethane-modified alkyd resins, silicone-modified alkyd resins, epoxide-modified alkyd resins, isophthalic acid alkyd resins, nonplasticized urea resins, plasticized urea resins, melamine resins, polyvinyl acetals, noncrosslinking P(M)A homo- and copolymers, noncrosslinking P(M)A homo- and copolymers with nonacrylic monomers, autocrosslinking P(M)A homo- and copolymers, P(M)A copolymers with other nonacrylic monomers, P(M)A homo- and copolymers which crosslink by means of external crosslinking agents, P(M)A copolymers with nonacrylic monomers and which crosslink by means of external crosslinking agents, acrylate copolymer resins, unsaturated hydrocarbon resins, cellulose compounds which are soluble in organic solvents, silicone combination resins, PU resins, P resins, peroxide-curing unsaturated synthetic resins, radiation-curing synthetic resins containing photoinitiator, radiation-curing synthetic resins without photoinitiator, and also solvent-free coating materials (binders), such as isocyanate-crosslinking saturated polyesters, PU 2-pack resin systems, moisture-curing PU 1-component resin systems, EP resins and plastics, individually or in combination, such as acrylonitrile-butadiene-styrene copolymers, cellulose acetate, cellulose acetobutyrate, cellulose acetopropionate, cellulose nitrate, cellulose propionate, artificial horn, epoxy resins, polyamide, polycarbonate, polyethylene, polybutylene terephthalate, poly-ethylene terephthalate, polymethyl methacrylate, polypropylene, polystyrene, polytetrafluoroethylene, polyvinyl chloride, polyvinylidene chloride, polyurethane, styrene-acrylonitrile copolymers, and unsaturated polyester resins as granules, powders or casting resin. By means of the pigments comprising oriented, three-dimensionally crosslinked substances with a liquid-crystalling structure having a chiral phase, the outstanding optical properties discussed above for the organosiloxanes, can for the first time be realized in countless applications using conventional techniques which are readily accessible to the person skilled in the art. The effects described are reassembled to a certain extent like a mosaic with each individual pigment in the binder system. By combining these pigments with one another and/or with conventional color pigments it is possible to achieve very diverse color effects on any desired surfaces, which, given by the completely transparent character of the liquid-crystal pigments in broad regions of the light spectrum, brings about a depth effect of the gloss exceeding any effects previously realized. Owing to their density, which is low in comparison with inorganic pigments, the pigments of the invention have a lesser tendency toward settling and separating in numerous binder systems. The present invention also relates to compositions which include pigments comprising oriented, three-dimensionally crosslinked substances with a liquid-crystalline structure having a chiral phase. Suitable starting substances for the preparation of the pigments according to the invention are liquid-crystalline substances which possess a twisted structure with a pitch corresponding to the wavelength of light in the range from UV to IR. Liquid-crystalline substances having a chiral phase, which possess a twisted structure with a desired pitch, may be obtained from nematic, smectic or discotic structures by adding a chiral substance to them. The nature and proportion of the chiral substance determine the pitch of the twisted structure and therefore the wavelength of the light reflected. The twisting of the structure may be either left-handed or right-handed. The starting substances must contain groups which can be polymerized by addition polymerization, polycondensation or polyaddition, at least some of which are in the form of difunctional, trifunctional or higher polyfunctional units. Examples of such systems are methacryloyloxy and acryloyloxy groups. Examples of suitable materials and their preparation are described in DE-C2-3,604,757, in EP-A2-358,208, in EP-A-0 066 137 (corresponding to U.S. Pat. No. 4,388,453), or in the literature cited by D. J. Broer et al., in 14. Int. Liquid Conf., Abstracts II, 921 (1992). Three-dimensionally crosslinkable polyorganosiloxanes as in EP-A-358,208 are preferably suitable. It is, however, possible in principle to use all cholesteric liquid crystals as starting substances for the preparation of the pigments according to the invention. One type of cholesteric liquid crystal or a mixture of at least two of these liquid crystals may be employed; one dye or mixtures of at least two dyes may be employed. In a preferred embodiment the dye to be employed is a pigment. In a further preferred embodiment the dye to be employed in the process according to the invention is soluble in the liquid crystal (mixture) used. In the process of the invention it is preferred to employ not a mixture of two or more cholesteric liquid-crystalline substances but rather a single, pure, cholesteric liquid-crystalline substance. Admixing of the pigments and/or dyes to the other starting substances takes place in a conventional manner, for example by adding them with stirring. In the pigment according to the invention, the admixing of the dyes and/or pigments results in a combination of the angle-dependent color effects of the liquid-crystalline substances with the known color effect(s) of the particular substances admixed. However, the admixing of these substances in no way alters the further process steps for the preparation of the pigments according to the invention. The pigment color desired in a particular case may also be obtained by mixing defined liquid-crystal base mixtures in appropriate quantitative ratios. In this case there is no change in the further process steps for the preparation of the pigments according to the invention. The further description of the preparation process therefore applies to all variants of the pigments according to the invention. Substances having a liquid-crystalline structure with twisted phases do not develop their optical characteristics until the individual molecules are arranged in layers and are uniformly ordered within a layer. The molecules change their preferred direction from layer to layer, so that helical structures are formed. In order to achieve this, the molecules are oriented by means of known methods, such as, by means of orientation layers or electric or magnetic field. Such methods are known from the following references: CA113 (22), 201523y; CA113 (14), 124523u; CA112 (18), 169216s; CA112( (16), 149138q; CA112 (4), 21552c; CA111 (16), 144258y; CA111 (4), 24780r. In the preparation of the pigments according to the invention the starting substances mentioned are oriented in a known manner. This can be accomplished, by knife-coating them onto a backing made of metal, plastic or glass. This backing may have been provided, if desired, with an orientation layer of polyimide or polyvinyl alcohol. If may also have been silanized for this purpose. However, it is also possible to shear the starting substance between two sheets. Preferably, one or two polyethylene terephthalate sheets are used. Orientation of the cholesteric liquid-crystalline molecules using two sheets leads to better orientation of the molecules and thus, ultimately, to pigments having an improved color effect. The knife-coating of liquid-crystalline polyorganosiloxanes onto a sheet is known, for example, from EP-A-358,208. Crosslinking of the oriented liquid-crystalline substances is carried out as disclosed for the material in question from the prior art. Thus, liquid-crystalline polyorganosiloxanes can be crosslinked thermally by the method described in EP-A-66 137. The liquid-crystalline polyorganosiloxanes described in EP-A-358 208 can be three-dimensionally crosslinked by photochemical means, for example by irradiation with UV light. A review of methods of crosslinking oriented starting materials photochemically can be found in C. G. Roffey, Photopolymerization of Surface Coatings, (1982) John Wiley & Sons, Chichester, pp. 137-208. The crosslinked oriented liquid-crystalline substances having a chiral phase are, if desired, removed from the backing. If a sheet is used as the backing, mechanical removal of the brittle crosslinked liquid crystals from the backing can be accomplished, for example, by guiding the backing over a deflecting roller of small diameter. This results in the crosslinked material flaking off from the sheet. However, any other method by which the polymerized material can be removed from the backing is also suitable. The oriented three-dimensionally crosslinked support-free liquid-crystalline material is comminuted to the particle size desired in each case. This can be effected by milling in universal mills or by rolling in roll apparatus. Depending on the desired application of the pigments, particles sizes having a diameter of from about 10 mm up to 1 .mu.m can be prepared. The pigments preferably have a particle size of between 500 .mu.m and 5 .mu.m. The pigments have a thickness of between 1 .mu.m and 20 .mu.m, preferably from 1 .mu.m to 15 .mu.m and more preferably from 3 .mu.m to 10 .mu.m. For pigments having a thickness of below 1 .mu.m effective color is weakened, whereas above a thickness of 20 .mu.m the homogeneous orientation of the molecules to cholesteric layers is reduced. In order to narrow the particle size distribution, the millbase can subsequently be classified, for example by screening. Pigments whose thickness is no different from the platelet diameter do not adopt a uniformly parallel orientation with respect to the surface in the binder systems or plastics, so that the cholesteric molecular layers present in the pigments are oriented in random spatial distribution. This results in a weakening of the angle-dependent color flop. Pigments having a very large platelet diameter may cause unevenness in the applied binder system, leading to a reduction in gloss. Consequently, as a result of their good processability, platelet-like pigments in particular having a layer thickness of from 3 .mu.m to 10 .mu.m and a platelet diameter of from 10 .mu.m to 100 .mu.m are particularly suitable for the above mentioned applications. Appropriate admixing of an organopolysiloxane with two monomeric substances to coloring formulations gives access to precursor materials for pigments of the entire visible spectral range, the only variation being in the proportions of the monomer substances added. It is possible to prepare pigments which cover a wide spectral range while at the same time having only marginal differences in their chemical and physical properties. Thus uniform test methods for this pigment class are possible for the particular application desired, leading to considerable savings in, for example, the application of production-line auto finishes. The entirely synthetic preparation of these precursor materials is regarded as a further advantage, since there are none of the fluctuations in quality which are observed, for example, with natural mica platelets from different deposits. The precursor materials of liquid-crystalline systems which are suitable for the preparation of the pigments according to the invention are based on organic starting materials, so that there are no problems with impurities, especially toxic impurities, as are encountered with inorganic materials, which may even in some circumstances lead to a reduction in the purity of color of the precursor material. The pigments according to the invention contain no problematic metals or compounds, with the result that no problems are to be expected even in the disposal of binder systems comprising pigments according to the invention. The specific optical properties of twisted layer systems occur only when the molecules have, in a defined temperature range, become oriented in layers which are twisted with respect to one another. A number of processes are suitable for this in the context of the present invention, and it is possible to employ even support-free methods which lead to the described orientation of the molecules. Because of the interference interaction with light, a plurality of mutually twisted layers lying on top of one another are required in order to obtain a high intensity of reflection. In this context, heterogeneities of layer thicknesses in the precursor film can be tolerated on condition that the molecules are oriented to form a helical layer. This is assured in the layer thickness range of a few .mu.m. For this reason the precise maintenance of a layer thickness in the range of a few .mu.m, in contrast to the processes for the preparation of multi-layer interference pigments, is not absolutely necessary for the preparation of the pigments according to the invention. The process steps for the preparation of the precursor film therefore permit relatively large tolerances for layer thicknesses. The pigments according to the invention with the viewing angle-dependent color impressions can be incorporated into water-thinnable coating systems or waterborne coating systems by using known methods to effect a dispersion which assures the uniform wetting of the pigments with the binder. Because of their chemical structure (organic materials) there are none of the problems with water (chemical reactions) which are observed in the case of many conventional inorganic pigments or metallic aluminum flakes. Moreover, the pigments according to the invention have no inherent electrical conductivity to interfere with specific applications and are resistant to alkalis and acid. Powder coating systems and high-solids systems are likewise suitable as binders into which the pigments of the invention can be incorporated, since, owing to the crosslinking reaction, the molecular layer structure of the pigments is preserved over a broad temperature range. In conventional solventborne coating systems such as nitrocelluloses, alkyd, thermoplastic-acrylic, urethane acrylic, polyurethane acrylic or polyester systems--whether they are physically and/or chemically drying systems--and in colored glazes of any desired composition, the color effects described can equally well be obtained. A particular advantage in photocrosslinkable coating systems is the fact that the pigments described are transparent over a broad wavelength range, since the light in the near UV region (UV A) which is required at the beginning of the photoreaction is not absorbed by the pigments. Furthermore, the pigments can be incorporated into natural resin coating materials or solvent-free coating materials or in binders as used in printing inks for screen printing or gravure printing. For the coating of metallic surfaces by means of the coil-coating method, the liquid-crystal pigments can be used without problems in acrylic ester, polyester or silicone-polyester coating systems. They can also be incorporated into plastics or into cosmetic products. In plastics, it is irrelevant whether they are incorporated into a casting resin, powder or granules. Examples of suitable systems are acrylonitrile-butadiene-styrene copolymers, cellulose acetate, cellulose acetobutyrate, cellulose acetopropionate, cellulose nitrate, cellulose propionate, artificial horn, epoxy resins, polyamide, polycarbonate, polyethylene, polybutylene terephthalate, polyethylene terephthalate, polymethyl methacrylate, polypropylene, polystyrene, polytetrafluoroethylene, polyvinyl chloride, polyvinylidene chloride, polyurethane, styrene-acrylonitrile copolymers, unsaturated polyester resins or combinations thereof. For the color effects described, achieved by means of the pigments according to the invention, to develop on any desired substrates it is necessary for the twisted molecular layers present in each individual pigment to be arranged as uniformly as possible over relatively large surface areas, resulting in a homogeneous spatial orientation of the helical axes. A homogeneous spatial orientation of the helical axes is assured in particular when the plateletlike pigments of the invention are aligned parallel to one another. The greater the shape factor, i.e., the greater the differentiation of two dimensions of a pigment from the third; the easier it is to achieve a highly uniform orientation of the pigments. It is therefore advantageous to employ, for the pigments which are incorporated into binders or other substances, processing methods which assure uniform orientation of the pigments according to the invention. It is not important whether these methods are manual or use automatic auxiliary equipment or are possibly employed, in addition, under electrostatic conditions. The pigments according to the invention which are incorporated into a binder system or into another material, for example a bulk medium, can be oriented by methods in which shear forces are exerted. Examples of such orientation methods are spraying, knife coating, rolling, brushing, air brushing, sprinkling, dipping, flow coating, printing (screen printing, gravure printing, pad printing, flexographic printing, offset printing), casting (rotomolding, injection molding), extrusion (single-screw extrusion, twin-screw extrusion, coextrusion), blowing (film blowing, blowmolding), calendering, dry coating, fluidized-bed sintering, triboelectric coating, electrostatic spraying, electrostatic coating, or lamination. More preferred orientation methods in binders are atomization, spraying, printing and knife coating. Use of these means of orienting pigment produces the angle-dependent color effect with helically polarized light just as well as on a cholesteric liquid-crystal layer applied to a planar substrate. If the pigments according to the invention are used to create color effects, then a great diversity of possible applications present themselves: in the vehicle sector (land vehicles, motor vehicles, rail vehicles, aircraft, water craft, bicycles) along with the accessories, in the leisure, sports and games sector, in the cosmetics sector, in the textile, leatherwear or jewelry sector, in the gift sector, in writing utensils, packaging or spectacle frames, in the construction sector (for example for interior walls, interior paneling, exterior facing, wall coverings, doors and windows) and in the household sector (for example for furniture, crockery, pots and pans and household implements). The pigments can also be used to obtain novel color effects in printed products of all kinds. for example cardboard and other packaging, carrier bags, paper products, labels and sheets. Owing to the transparent properties of the pigments in all binder systems and bulk systems, an impression similar to pearl luster pigments of deep gloss of previously unobtained intensity, is manifested in an extremely high perception of brilliance even under poor light conditions. The pronounced angle-dependent color effects with polarization of light can also be employed to particularly good effect in the area of security marking and of protection against forged color copies. Owing to the diversity of the reflection wavelengths which can be obtained, from the UV to the IR region, and to the possible combinations of diverse pigments of the invention with one another and with other pigments, it is possible to secure against forgery documents of all kinds, bank notes, check cards or other cashless means of payment or certificates. Since the pigments of the invention can be processed by known printing techniques, it is possible to produce data carriers with security elements which offer the same advantages as those described in DE 39 42 66 31 A1. The pigments according to the invention make it much easier to produce such data carriers. The invention therefore also relates to data carriers comprising pigments according to the invention. Objects coated with conventional absorption pigments have a dull appearance, whereas the same objects appear to be "alive" when coated with a layer of paint into which pigments of the invention having the same color have been incorporated. Using specific color combinations it is possible to intensify or to attenuate the angle-dependent color effets. Depending on the function of the pigments according to the invention, there are a number of possible layer structures with which the desired effects can be achieved. The simplest system is a one-layer structure in which the pigments is incorporated into a binder and applied. This is possible especially for layer thicknesses above 10 .mu.m to 20 .mu.m, for example in the screen printing technique. However, a binder surface whose shape is not ideally smooth results in diffuse reflection at the interface between binder and air, so that the directed reflection brought about by the pigments according to the invention is overlaid by the diffuse reflection, leading to an attenuation of the color effect. This disadvantage can be countered by covering the pigment-binder layer with a clear coat, leading to brilliant color effects which are substantially more pronounced. The color effects may be further intensified by placing chromophoric layer beneath the two-layer system consisting of novel pigment in binder and of clear coat. An alternative option is to incorporate further color pigments into the binder, so that the hiding power is increased and the color effects described can be obtained independently of the color of the substrate. The only requirement is to ensure that the pigments of the invention in the dry binder system are not completely covered by absorbing pigments which face the light source. If pigments of the invention which reflect in different wavelength regions are mixed in the binder system, then it is possible to produce color effects from composite colors of the individual pigments. By adding metallic pigments (for example aluminum flakes) or pearl luster pigments, the effects lead, depending on the weighting of the individual classes, to surprising results. Depending on the application the pigments of the invention may be prepared and employed in a very wide range of particle sizes and particle-size distributions. Coarse particles, for example those having a platelet diameter of greater than 100 .mu.m, bring about a tinsel like, glittering effect without any pronounced hiding power. Finely ground particles on the other hand, for example those having a platelet diameter of about 10 .mu.m, give a hiding power with reduced specific brilliance, especially when they are not arranged parallel to one another in the binder system and when the helical axes of the cholesterically configured layers are arranged heterogeneously in space. By the combination of both effects it is thus possible to obtain a high hiding power in conjunction with a glitter effect which resembles brilliance. In such systems the color changes depending on the viewing angle, an effect which is particularly highly pronounced for curved, moving objects. Pretreated substrates (for example functional layers such as rustproofing coats) can also be provided with the optical effects in accordance with the structure described. The following examples serve to illustrate the invention in more detail. Examples 1 to 4 describe pigment preparation, Examples 5 to 12 describe representatives of different binder system, Examples 13 to 18 describe methods for the orientation of the pigments according to the invention in binder system, and Examples 19 to 25 describe applications of the pigments of the invention in a special-effect function. Examples 26 to 35 present different color layer systems |
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