CA2189236C - Coating compositions whose perceived colour depends on the angle from which they are viewed and the use of such compositions in base paints for multiple layer paint coatings - Google Patents

Abstract

Coating compositions are disclosed, suitable for use as base paints for multiple layer coatings, whose perceived colour depends on the angle from which they are viewed. They contain: one or more binders usually used in such coatings; one or more scale-type pigments the hue of which depends on the angle from which they are viewed, these pigments consisting of oriented, three-dimensionally cross-linked substances of chiral phase, liquid crystalline structure; one or more usual effect pigments which differ from the said scale-type pigments;
optionally one or more cross-linking agents; optionally one or more colour-imparting absorption pigments and/or fillers; and optionally additives usually used in coatings of this type.

Description

Coating- eomy~osition whose ",rerceived color dey~ends on the viewingr_ ancle, and use thereof in basecoats for multi-coat paint systems The invention relates to coating compositions which are suitable for producing coatings having a perceived color which is particularly bright and depends on the viewing angle. These coating compositions are, in particular, basecoats.
Coating compositions which permit the production of coatings whose perceived color is dependent on the angle of :incident light and/or on the viewing angle are known, in particular, as effect basecoats. In the context of effect basecoats, there is the requirement for a continually increasing number of effect colors. The effect basecoats comprise plateletlike special-effect pigments which bring about a so-called brightness flop and/or color flop. On the basis of pure metal flake pigments for producing a brightness flop, for example those of aluminum, a large number of further plateietlike special-effect pigments have been developed which are suitable for use in effect basecoats. Examples of further plateletlike special-effect pigments are interference pigments, for example metal pigments coated with metal oxide, an example being aluminum coated with titanium d.i oxide or with mixed oxide, and coated micas, for instance micas coated with titanium dio~:ide, and graphite special-effect pigments. It is also common to combine such special-effect pigments with one another; for example, aluminum Bake pigments are combined with mica-based interference pigments in effect basecoats .or vehic~e finishing. Lsing the known interference pigments, cnly a relat~.vely weak color flc>p can be dbtained.
German Patent App:Lication P 42 40 743.5 published June 9, 1994 describes pigments whose ,.

color depends on the viewing angle, which consist of oriented, three-dimensionally crosslinked substances having a liquid-crystalline structure with a chiral phase.
EP-A-0 357 844 describes water-dilutable coating compositions which comprise a combination of flop effect pigments and encapsulated, thermochromic, liquid-crystal pigments. Coat:_ngs produced therewith change their perceived color z-eversibly in dependence on the temperature.
The object of the invention is to provide coating compositions, especial:Ly basecoats, and which permit the production of coatings with novel color effects, in which context their perceived color is to be independent of the temperature.
It has been found that this object can be achieved by a coating composition which is suitable as a basecoat for multicoat paint systems and comprises:
- one or more customary paint. binders, - one or more plateletlike: pigments whose color depends on the viewing angle, which consist of oriented, three-dimen:~ionally crosslinked substances of liquid-crystalline structure with a chiral phase, - one or more customary special-effect pigments which differ therefrom, - if desired, one or more crosslinking agents, - if desired, one or more colored absorption pigments and/or fillers, and - if desired, customary paint additives.
The pigments whose color depends on the viewing angle, which consist of oriented, three-dimensionally crosslinked substances of liquid-crystalline structure with a chiral phase, are referred to below as LCP
pigments LCP - liquid crystal polymeri. The LCP
pigments can be obtained by subjecting one or more three-dimensionally crosslinkable liquid-crystalline substances with a chiral phase to orientation, then to three-dimensional crosslinking and subsequently to r_ 2189236 comminution to the desired particle size. This can be carried out, for example, by first applying the three-dimensionally crosslinkable liquid-crystalline sub-stances with a chiral phase to a substrate in a thin layer, for example by knife coating, crosslinking the layer on this substrate, then detaching it from the substrate and comminuting i.t to the desired particle fineness. This produces plateletlike pigments which are transparent and colorless per se. By means of appropriate chemical stru<aure-forming measures in relation to the molecular structure, LCP pigments having different effective interference colors can be produced. The plateletlike LCP pigments preferably have a diameter of from 1 to 100 Vim, particularly preferably from 10 to 60 Vim, and a thi~~kness of preferably from 3 to 15 Vim, particularly preferably from 5 to 10 Vim.
In accordance with the invention it is possible, for example, to use those LCP pigments as described in the German Patent Application P 42 40 743.5, to which reference is hereby made. Reference is also made here to the starting substances for the preparation of the LCP pigments, and details on the preparation techniques, which are described therein.
In accordance with German Patent Application P 42 40 743.5, liquid-crystalline substances which are suitable as starting substances for the preparation of the LCP pigments have a twi;ated structure with a pitch which corresponds to a wavelength of light in the range from W to IR. This structure is found, for example, in cholesteric liquid crystals. Cholesteric liquid crystals, or, in general, liquid-crystalline substances with a chiral phase, which ;possess a twisted structure with a desired pitch, can be obtained from nematic, smectic or ciscctic struorures by adding to them a chiral substance. '.'he nature and proportion of the chiral substance determine the pitch of the twisted structure and therefore the wavelength of the reflected light. The twisting of the structure may be either ~~ $~~~6 - 4 ~-left-handed or right-handed. The starting substances must additionally comprise groups which can be polymerized by addition polymerization, condensation polymerization or polyaddition and of which at least some are in the form of difunctional, trifunctional or more highly functional units. Examples of such groups are methacryloxy and acryloxy groups.
Examples of suitable materials and their preparation are described, for example, in DE-C2 3 604 757, in EP-A2-358 208, i.n EP-A-0 066 137 (corres ponds to US 4 388 453) or in the literature cited in D. J. Broer et al . in 14th Int . Liquid Conf . , Abstracts II, 921 (1992).
Three-dimensionally crosslinkable polyorgano siloxanes which are preferably suitable are those according to EP-A-0 358 208.
As starting materials for the preparation of the LCP pigments, however, it is possible in principle to use all cholesteric liquid crystals. It is possible to employ one type of cholesteric liquid crystal, or else a mixture of at least two of these liquid crystals. In addition to these liquid crystals, other dyes and/or pigments can be used as further components in the preparation of the LCP pigments. It is possible to employ one colorant or else mixtures of at least two colorants.
In a preferred embodiment, the colorant to be employed is a pigment, for example gas black. The colorant to be employed is, in a further preferred embodiment, soluble in the :Liquid crystal (mixture) employed. Preference is given to the employment not of a mixture of two or more cholesteric liquid-crystalline substances but of a single, pure, cholesteric liquid-crystalline substance.
The admixing of the pigments and/o.w dyes to the other starting substances is carried out in a customary manner, for example by incorporation with stirring. The admixing of the dyes and/or pigments brings about, within the LCP pigment, a combination of the angle-dependent color effects of the liquid-crystalline substances with the known color effects) of the respective substances admixed. The admixing of these substances does not, however, alter the subsequent process steps for the preparation of the LCP pigments.
A particularly desired LCP pigment color can also be obtained by mixing defined liquid-crystal base mixtures in appropriate proportions. In this case too, there is no change in the subsequent process steps for the preparation of the LCP pigments. The subsequent description of the preparation process, therefore, applies to all variants of the ~~CP pigments.
Liquid crystals with twisted phases C~PVP1 fl Y1 t.'~eir optical properties only when the individual molecules are arranged in layers and are ordered uniformly within a layer. In this context, the molecules change their preferential direction from layer to layer, producing helical structures as a result. In order to achieve this, the molecules are aligned (oriented) by means of known methods, for example by alignment layers or electrical or magnetic fields. Such methods are known, for example, from the following references: CA113 (22), 201523y: CA113 (14), 124523u; CA112 (18), 169216s; CA112 (16), 149138q;
CA112 (4), 21552c; CAlll (16), 144258y; CAll1 (4), 24780r.
In the course of the preparation of the LCP
pigments, the starting substances cited as examples are oriented in a known manner. This can be accomplished, for example, by knife coating onto a metal, plastics or glass substrate. The knife coating of liquid-crystalline,polyorganosiloxanes onto a film is known, for example, from ~P-A-0 358 20E3.
The oriented liquid-cr~~stalline substances are crosslinked as is known from the prior art for the respective material. For example, liquid-crystalline polyorganosiloxanes can be crosslinked thermally by the method described in EP-A-0 066 137. The liquid crystalline polyorganosiloxanes described in EP-A

0 358 208 can be three-dimensionally crosslinked photochemically, for example by irradiation with W
light. An overview of methods for the photochemical crosslinking of oriented starting materials can be found in C.G. Roffey, Photopolymerization of Surface Coatings (1982), John Wiley b: Sons, Chichester, pp.
137-208.
Examples of special-ef:Eect pigments which can be used in addition to the LCP pigments in the novel coating composition, generall~r plateletlike special-effect pigments, are the customary pigments used, for example, in effect coating materials, such as metal pigments, for example of titanium, aluminum or copper, interference pigments, such as metal oxide-coated metal pigments, for example titanium dioxide-coated or mixed-oxide-coated aluminum, coated mica, for example titanium dioxide-coated or mixed-oxide-coated mica, microtitanium dioxide and graphite special-effect pigments, plateletlike iron oxide (micaceous iron oxide), molybdenum disulfide pigments, plateletlike copper phthalocyanine pigments and bismuth oxychloride flakes, and coated glass flakes. It is possible for the mixed-oxide-coated aluminum pigments and mica pigments to have a covering of organic p_Lgments.
The particular perceived color or color effect of the coatings produced from ~~he coating compositions according to the invention i:~ a result of parallel alignment of the plateletlike :GCP pigments and of the further special-effect piginent;s in the coating fi lm.
The regular structure of the LCP pigments and the uniform molecular arrangement within these liquid-crystalline units gives rise to considerable interference phenomena with t:he incident light. As these phenomena are overlayed with the customary color properties of the further effE~ct-imparting component, the perceived color changes not only depending on the incident angle of the light but also, in addition, on the viewing angle. When viewing a three-dimensional article with such a coating, for example, this results _ 7 _ in a perceived color which varies over the entire article.
The coating composit~.on according to the invention may be physicall~~ drying or may be crosslinkable with the formation of covalent bonds. The coating compositions which crosslink with the formation of covalent bonds may be autocrosslinking or externally crosslinking systems. The systE~ms may comprise one or two components. They may be aqueous or solvent-based coating compositions.
The aqueous coating compositions according to the invention comprise water-dilutable binders. To assure their dilutability in water, these binders comprise nonionic and/or ionic groups which impart hydrophilicity.
Examples of suitable nonionically stabilized binders are those binders whose dilutability in water is achieved by the incorporation of polyether segments into the resin molecule. Examples of polyurethane resins or polyurethane acrylat:e resins stabilized in this way are described in EP-A-0 354 261, EP-A-0 422 357 and EP-A-424 705.
The water-dilutable binders which carry ionic groups may be binders carrying cationic or anionic groups.
Examples of appropriate cationically stabilized binders are described in DE--A-40 11 633. These are completely or partially neutralized, cationic, (meth)acrylic copolymer resins, polyester resins, polyurethane resins and/or polyurethaneurea resins, especially those having a number-average molar mass (Mn) of from 500 to 500, 000, an OH number of from 0 to 450, an amine number of from 20 to 200 and a glass transition temperature of from -50 to +150°C.
Pz::ferred binders arE~ those stabilized by anionic groups. They comprise one or more film-forming resins as are customary in aqueous coating compositions, especially in aqueous basecoats. The film-forming resins can, for e~;ample, have a polyester, (meth)acrylic copolymer or, preferably, a polyurethane basis. They may be autocrosslinking, externally crosslinking or physically drying. Examples of appropriate water-dilutable (meth)acrylic copolymers are described in EP-A-0 399 427 and EP-A-0 287 144.
Examples of appropriate water-dilutable polyester resins are described :in DE-A-29 26 854, DE-A-38 32 142 and EP-A-0 301 300.
It is also possible to employ mixtures of binders. Particularly suitable binders are those in which (meth)acrylic copolymer and polycondensation resin are present bonded covale:ntly or in the form of interpenetrating resin molecules. Examples of such a combination of (meth)acrylic copolymer and polyester resin which can be used are described in EP-A-0 226 171.
Examples of the anionically stabilized polyurethane resins which are particularly preferred are described in great diversity in the literature.
These are aqueous polyurethane dispersions or polyurethane solutions, or binders in which (meth)acrylic copolymer and ~~olyurethane resin are present bonded covalently ~~r in the form of interpenetrating resin molecules. Suitable polyurethane dispersions are stable, aqueous dispersions with a solids content of from 20 to 50o by weight. The weight-average molar mass (Mw) of the resins can vary within wide limits, for example from 1000 to 500,000.
Further examples of Polyurethane dispersions which can be used are those which can be prepared by the chain extension of isocyanate-functional prepolymers with polyamine and/or polyol. They are described, for example, in EP-A-0 089 497, EP-A
0 228 003, DE-A-36 28 124 and El?-A-0 512 524.
Further examples are polyurethane dispersions which can be prepared by the chain extension of isocyanate-functional prepolymers with water, as set out, for example, in DE-A-39 15 459 and DE-A-42 24 617.

- 9 _ 2189236 It is also possible to use polyurethane dispersions which are prepared by the chain extension of polyisocyanate-reactive polyurethane prepolymers which contain active hydrogen with polyisocyanates, as described, for example, in DE;-A-39 03 804 and DE-A-40 O1 841. -Further examples of anionically stabilized polyurethane (PU) dispersions which can be used are described in DE-A-42 28 510. These are aqueous polyurethane dispersions which are obtainable by the chain extension of one or more polyurethane resins comprising at least one CH-acidic group in the molecule, by reaction in aqueous or nonaqueous medium with - at least one compound which is able to react with at least two CH-acidic groups, and - if desired, transfer of a reaction product obtained in a nonaqueous medium to the aqueous phase.
Examples of anionically stabilized, polyurethane-based binders in which (meth)acrylic copolymer and polyurethane resin are present bonded covalently or in the form of interpenetrating resin molecules are described, for example, in EP-A-0 353 797, EP-A-0 297 576, DE--A-41 22 265 and DE-A
41 22 266. These are polymer hybrids prepared by emulsion polymerization of free-radically polymerizable monomers in the presence of anionically stabilized polyurethanes, which may also be functionalized with unsaturated functions.
The coating compositions according to the invention can comprise an aqueous binder, or else two or more aqueous binders can be present in combination.
Preferably, the aaueous coating compositions according to the invention comprise aqueous binc:~=rs based on anionically stabilized polyurethanes. It may be expedient for some, for example up to 50% by weight, of the polyurethane binders to be replaced by resins based on a combination of (meth)acrylic copolymer and polyester resin.
It is also possible for water-dilutable binders based on cellulose to be present.
The novel solvent-based coating compositions comprise binders which are dispersed or dissolved in organic solvents. As film-forming binders it is possible, for example, for polyester resin, alkyd resin, polyurethane resins, poly(meth)acrylate resins and/or resins based on cellulose esters, for example cellulose acetobutyrate, to be present. Examples of such binder systems which can be employed in the novel coating composition are described in EP-A-0 289 997, WO-,0.100 895, DE-A-37 15 254, DE-A-39 13 001, DE-A-41 15 948 and DE-A-42 18 106.
To prepare the coating compositions according to the invention it is possible to use various crosslinking agents, such as, f:or example, formaldehyde condensation resins, such as phenol-formaldehyde condensation resins and amine-formaldehyde condensation resins, and also free or bloc'.ted polyisocyanates. The crosslinking agents can be employed individually and as a mixture. The mixing ratio of crosslinking agent to binder resin is preferably from 10:90 to 40:60, particularly preferably from 20:80 to 30:70, based in each case on the weight of solids.
Amine resins which are suitable crosslinking agents include, for example, alkylated condensation products prepared by react:.ng aminotriazines and amidotriazines with aldehydes. In accordance with known technical processes, amines or compounds carrying amino groups, such as melamine, gu~anamine, acetoguanamine, benzoguanamine, dicyandiamide or urea, are subjected to condensation in the presence of alcohols, such as methanol, ethanol, propanol, butanol or hexanol, with aldehydes, especially formaldehyde. Examples of such resins and their preparation are described in Houben-Weyl, Methoden der organischen Chemie, 1963, page 357.
These products are available commercially.

-~~-It is possible to employ free or blocked polyisocyanates as crosslinking agents. The polyisocyanates are any desired organic diisocyanates and/or polyisocyanates having free isocyanate groups which are attached to aliphatic, cycloaliphatic, araliphatic and/or, less preferably, to aromatic structures and which are liquid at room temperature or are liquefied by adding organic solvents or which, in dissolved form at 23°C, general:Ly have a viscosity of from 0.5 to 2000 mPas, preferably of more than 1 and below 1000 mPas, particularly preferably below 200 mPas. Preferred diisocyanates are those containing from about 3 to about 36 carbon atoms, in particular from about 8 to 15 carbon atomso. Examples of suitable diisocyanates are hexametlzylene diisocyanate, tetramethylxylylene diisoc~~anate, isophorone diisocyanate and dicyclohexylmethane diisocyanate.
Preference is given t:o the use of poly isocyanates of relatively high isocyanate func tionality, for example polyisocyanates prepared by di and/or trimerization of the abovementioned diiso-cyanates. Further examples are polyisocyanates which contain biuret groups and are prepared by reacting the abovementioned diisocyanates with water, or polyisocyanates which contain urethane groups and are prepared by reaction with polyols.
In the case of the blocked polyisocyanates, it is possible to use any desired organic polyisocyanates which are suitable for crosslin:king, for example those mentioned above, in which the isocyanate groups have been reacted with a compound such that the blocked polyisocyanate formed is resistant to hydroxyl groups and water at room temperature but reacts at elevated temperatures, in general in the range from about 90 to about 250°C.
The blocked polyisocyanates which can be employed as crosslinking agents can be blocked with customary, volatile, monovalent blocking agents as are employed, for example, in paint chemistry. Examples thereof are various alcohols, oximes, phenols, amines, beta-keto compounds, phthalimide, etc. Within a molecule, the polyisocyanates can be blocked with identical or different blocking agents. As crosslinking agents it is also possible to use mixtures of differently blocked polyisocyanates, and also polyisocyanates which are blocked differently within the molecule.
The coating compositions according to the invention can additionally comprise polymer micro particles which are known to the person skilled in the art and are customary in the paints sector. Crosslinked or noncrosslinked micropartic:Les can be employed.
Examples of such polymer microparticles are described in EP-A-0 038 127 and EP-A-0 234 362.
The coating compositions can additionally comprise technical paint additives, for example agents which influence the rheology, such as highly disperse silicic acid, inorganic phyllosilicates or polymeric urea compounds. Examples of other effective thickeners in the aqueous coating compositions according to the invention are water-soluble ce::lulose ethers, such as hydroxyethylcellulose, methylcellulose or carboxymethylcellulose, and synthetic polymers having ionic groups and/or groups with an associated action, such as polyvinyl alcohol, poly(meth)acrylamide, poly(meth)acrylic acid, polyvinylpyrrolidone, styrene-maleic anhydride or ethylene- malefic anhydride copolymers and their derivatives, or else hydrophobically modified, ethoxylated polyurethanes or polyacrylates. It is also possible to employ antisettling agents, leveling agents, light stabilizers (for example of the HALS type', of the benzotriazole type, micro-titanium dioxide), antifoams, for example silicone-:~ntaining compounds, wetting agents, and adhesion-promoting substances. In order to accelerate curing, it is possible if desired to employ catalysts.
Small amounts of solvents, for example customary technical paint. solvents, may also be present w _ 2189236 in the aqueous coating compositions according to the invention. These solvents can come from the preparation of the binders or are added separately. Examples of such solvents are mono- or polyhydric alcohols, for example propanol, butanol and hexanol~ glycol ethers or glycol esters, for example diethylene glycol dialkyl ethers, dipropylene glycol dia7.ky1 ethers, each with C1-C6-alkyl, ethoxypropanol and butylglycol; glycols, for example ethylene glycol, propylene glycol and oligomers thereof, N-methylpyrrolidone, and ketones such as methyl ethyl ketone, acetone and cyclohexanone;
aromatic or aliphatic hydrocarbons, for example toluene and xylene, or linear or branched, aliphatic, C6-C12 hydrocarbons.
The nonaqueous coating compositions according to the invention contain customary organic paint solvents, for example aromatic compounds, such as toluene, xylenes, ethylbenzene, Solvesso 100~ (mixture of aromatic hydrocarbons having ;3 boiling range of from 153 to 180°C); esters, for examp.Le ethyl acetate, butyl acetate, amyl acetate; glycol ether esters, for example ethoxypropyl acetate, ethyl glycol acetate, methoxypropyl acetate; glycol ethers, for example ethylene glycol dimethyl ether; ketones, for example methyl ethyl ketone, diisobutyl ketone, cyclohexanone, isophorone; and alcohols, for example propanol, hexanol, isobutanol.
By way of the choice of :solvents it is possible to influence the flow and viscosity of the coating composition. By way of the boiling point of the solvent mixture employed, it is possible to influence the evaporation properties.
The coating composition according to the invention comprises at least one LCP pigment, at least one further plateletlike special--effect pigment and, if desired, one or more inorganic and/or organic color-imparting absorption pigments, if desired one or more fillers, and also, if desired, one or more soluble organic dyes. The absorption pigments and dyes are preferably dark in nature, since then the special color effect aimed at in accordance with the invention is reinforced to a particular degree. The absorption pigments and dyes can, with regard to their color, be adapted to the effective interference color of the LCP
pigment or can differ from it. l?referably, the coating composition according to the invention comprises only one LCP pigment and only one: further plateletlike special-effect pigment. However, it is also possible to employ mixtures of LCP pigments of different effective interference colors and mixtures of further special-effect pigments. Preferably, no additional dyes or absorption pigments are present. By way of the mixing of a plurality of LCP pigments with different effective interference colors, there are no limits on the establishment of all conceivable shades of color.
Examples of color-imparting absorption pigments and/or fillers, which may be organic or inorganic in nature, are titanium dioxide, iron oxide pigments, carbon black, silicon dioxide, barium sulfate, talc, azo pigments, phthalocyanine pigments, quinacridone pigments or pyrrolopyrrole pigments.
In the case of nonaqueous coating compositions according to the invention, the LCP pigments are incorporated directly by stirring into the binder present in organic phase. The further special-effect pigments are incorporated into t:he coating composition, for example, as follows: interference pigments are incorporated similarly to the LCP pigments, whereas metal flake pigments in the f~~rm, for example, of a customary commercial paste are first of all suspended in an appropriate solvent, for example in one of the abovementioned solvents, before being added to the binder present in organic phase.
The color-imparting ab~.orption p.4gments and/or fillers are generally dispersed in a portion of the binders, or dispersion can be carried out in a specific paste resin. Dispersion takes place in customary equipment which is known to the person skilled in the art. Subsequently, the finished color pigment dispersion is made up with the :remainder of the binder or of the paste resin.
In the case of aqueous coating compositions, the pulverulent LCP pigments are first of all processed with preferably water-dilutable organic solvents and additives to form a paste. In preparing the paste, it may be expedient to add the above-described water dilutable binders and/or a paste resin. The further special-effect pigments are introduced first of all, in the form for example of a customary commercial paste, water-dilutable organic solvent and additives are added to them, and then this composition is mixed with the aqueous resin solution, with shearing. Pulverulent special-effect pigments are first of all processed with solvent and additives to form a paste.
The color-imparting absorption pigments and/or fillers are generally dispersed in a portion of the water-dilutable binders. Dispersion can also, preferably, take place in a specific water-dilutable paste resin. One example of a paste resin which is based on an anionically stabilized polyurethane resin and which can be employed with preference in the aqueous basecoat according to the invention can be found in DE-A-40 00 889. Dispersion takes place in customary equipment which is known to the person skilled in the art. Subsequently, the finished color-pigment dispersion is made up with the remainder of the aqueous binder or of the aqueou:~ paste resin.
when processing the plateletlike LCP pigments and the further special-effect pigments, care should be taken that these pigments are not damaged mechanically during the mixing operation.
If paste resins are present in the coating composition, they add to binder plus any crosslinking agent present.
Where the basecoats according to the invention are aqueous basecoats formulated on the basis of cationically stabilized binders, they contain acids as - li; -neutralizing agents. Examples are formic acid, acetic acid and lactic acid.
Where the basecoats according to the invention are aqueous basecoats formulated on the basis of anionically stabilized binders, they contain bases as neutralizing agents. Examples are ammonia or organic amines, such as triethylam:W e, N-methylmorpholine, or amino alcohois such as dimethylisopropanolamine, dimethylethanolamine and 2-amino-2-methyl-1-propanol.
The coating compositions according to the invention can be provided, :Eor example, in the form of a mixer system consisting of mix coating materials.
The basecoats according to the invention can also be prepared in the form of so-called modules, from which the basecoats are ultimately prepared by mixing directly before use. For example, the LCP pigments and the further special-effect pigments can be part of an effect module. In addition, for example, the binders can be part of a binder module and, if desired, of a color module and/or effect module prepared separately therefrom. The crosslinking agents, for example, can be part of a crosslinking module. Other constituents can be present in the form of further separate modules. An example of an aqueous modular system of this kind is described in German Patent Application P 43 O1 991 from the same applicant published July 28, 1994.
The coating composition according to the invention, for example a basecoat according to the invention, has a solids content which is, for example, from 10 to 50% by weight, ~~referably from 15 to 30% by weight. The ratio of pigment to binder in the coating composition according to t:he invention is preferably prom 0.03:1 to 1:1, particularly preferably from 0.06:1 to 0.5:1, based in each case on the weight of solids.
The ratio of LCP pigment plus further special-effect pigment to binder in the coating composition according to the invention is preferably from 0.03:1 to 0.5:1, particularly preferably from 0.06:1 to 0.25:1. The volume ratio of LCP pigment to further special-effect A:

pigment is preferably from 1:10 and 10:1. In the abovementioned data relating to the weight ratios, the term "binder" comprises the b:~nder as such plus any crosslinking agent present plus any paste resin present.
The coating compositions according to the invention can be applied by cuss=omary methods. They are preferably applied by spraying in a dry-film thickness of, for example, from 15 to 40 ~.m. When used as basecoats for the production of multicoat paint systems, they are preferably applied by the wet-on-wet technique; in other words, after a flash-off phase, for example at from 20 to 80°C, th~~ basecoat films can be overcoated with a customary clearcoat in a dry-film thickness of preferably from 30 to 80 ~.m and the two coats can be dried together or crosslinked at temperatures of, for example, from 20 to 140°C. The drying conditions of the topcoat layer (basecoat and clearcoat) depend on the clearcoat system used. They may, for example, be from 20 to 150°C. For refinish purposes, temperatures of from a0 to 80°C, for example, are preferred. For production-line finishing, preferred temperatures are generally above 80°C, for example above 100°C. Suitable clearcoats are, in principle, all known clearcoats or coating compositions pigmented with transparent pigments. In this case it is possible to employ either solvent-containin~3 one-component or two-component coating materials, wat=er-dilutable clearcoats or powder clearcoats. It may be. expedient to choose a clearcoat thickness which is in the region above 50 Vim, for example by applying two cle:arcoat films comprising identical or different liquid clearcoats, or a corresponding powder clearcoat film. These multicoat paint systems can be applied to various kinds of substrate. The substrates are generally metallic or plastics substrates, and are frequently precoated; that is to say that plastics substrates, for example, can be provided with a polymer primer, metallic substrates genera-lly possess an electrophoretically applied primer _. 2189236 and, if desired, one or more f~.zrther coats in addition, for example a filler coat. In general, these coats are cured.
The substrates to be coated with the coating composition according to the invention are preferably dark substrates. The term substrate in this context is to be understood not only as a substrate which is provided on its surface with a dark coat of paint but also a substrate, for example a plastics substrate, with inherently dark pigmentation. Examples of dark coats of paint are primers, for example primers applied electrophoretically or by spray painting, polymer primers, filler coats or anti-stonechip coats, or else solid-color basecoats or topcoats. The dark substrates or dark coats of paint are pigmented with dark absorption pigments, special-effect pigments being expressly excluded. Examples of dark substrates are those which are dark blue, dark red, dark green or, preferably, dark gray, with black being particularly preferred. In such cases, the effect aimed at with the coating composition according to the invention stands out with particular distinction. The coating compo-sitions according to the invention can, of course, also be applied to substrates with a relatively light color, but then the special color effect aimed at in accordance with the invention is effective only to a lesser extent.
The coating composition according to the invention permits the production of bright-colored multicoat paint systems with a surprisingly strongly pronounced color flop, which is overlaid by the customary color properties of the further effect-imparting components which are present in the coating composition in addition to the LCP pigments. The perceived color of the 'rinished substrates changes in dependence on the incident angle of the light and, in addition, on the viewing angle, but is independent of external temperature effects.

The multicoat paint sysr_ems obtained using the coating compositions according to the invention meet the requirements which are nowadays customary in the finishing of automobiles. The: coating compositions according to the invention are therefore suitable for the OEM finishing and refinishing of vehicles, especially as a basecoat, but c:an also be employed in other sectors, for example in the painting of plastics, especially the painting of automotive components.
Example l,i Polyiaanos~~oYanes with metha ~rloxl-functional side chains A solution of 233 g of 4-(prop-2-en-1-oxy)ben zoic acid cholesterol ester (obtainable in accordance with DE-A-3 110 048), 178 g of 4-trimethylsiloxyphenyl 4-(prop-2-en-1-oxy)benzoate (obtainable in accordance with EP-A-0 358 208, page 9, Section C) and 56.9 g of tetramethylcyclotetrasiloxane in 400 ml of toluene was boiled under reflux in the presence of 24 mg of dicyclopentadiene platinum dichloride for 1 hour and, following the addition of a solution of 1.2 g of NaOH
in 50 ml of ethanol, for a further 7 hours, in order to cleave the silyl ether. The reaction mixture was concentrated to 1/3 of its volume in a rotary evaporator, 7.5 g of p-toluenesulfonic acid and 154 g of methacrylic anhydride were added, and the mixture was heated at 100°C for 1 hour. After removal of the volatile constituents by distillation, the residue was reprecipitated twice from methy7.ene chloride/ethanol.
The product had the following physical and thermodynamic data:
Glass transition point: 14°C, cJ_earing point: 141°C.
Examrle 2:
pre~arat~on of a solymerizable monomer 4-ethylphenyl methacryloxybenzoate A solution of 16.9 g of 4-ethylphenyl 4-tri-methylsilyloxybenzoate (prepared according to the instructions in EP-A-0 358 208, page 9, section C) in 15 ml of toluene and 10 ml of ethanol was boiled under reflux for one hour and then freed from volatile constituents by heating at 100°C for 60 minutes. The 13.3 g of 4-ethylphenyl 4-hydroxybenzoate which remained were dissolved, together with 30 g of methacrylic anhydride and 1.2 g of toluenesulfonic acid, in 15 ml of toluene and the solution was heated at 100°C for 1 hour. After c~~oling, the product was precipitated with hexane and recrystallized from ethanol.
Exaa~gle 3:
prA~arat-; r,~ of a red liquid-crystal mixture 6 g of the polyorgano:~iloxane prepared as in Example 1 were dissolved in 50 ml of toluene . 1 . 5 g of 4-ethylphenyl methacryloxyben2;oate (prepared as in Example 2) and 7.5 mg of aluminum cupferron (obtainable under the name Q 1301 from Wako Chemicals GmbH, Neuss) were added to this solution. The toluene was then removed at 70°C under vacuum in a rotary evaporator.
A viscous LC mass is formed which has the following physical and thermodynamic data:
Glass transition point: -2°C, clearing point: 124°C.
E~sle 4:
prps,arat-~ ~n of a blue licruid-cr5rstal mixture 6 g of the polyorganosiloxane were prepared as described in Example 1. This was dissolved in 50 ml of toluene. 2.6 g of methacrylic acid cholesterol ester (prepared as in De Visser et al., J. Polym. Sci., A
1(9), 1893 (1971)) and 9 mg of aluminum cupferron (obtainable under the name Q 1301 from Wako Chemicals GmbH, Neuss) were added to this solution. The toluene was then removed at 70°C under vacuum in the rotary evaporator.
A viscous LC mass was formed which has the following physical and thermod~rnamic data:
Glass transition point: 4°C, clearing point: 132°C.

y:~. ~ 2189236 - 21. -le 5:
~) Preparation of a green licruid-crvatal mixture 2.8 g of the red color mixture (prepared as described in Example 3), 1.2 g of the blue color mixture (prepared as described in Example 4) and 0.11 g of 2-methyl-1-[4-(methylt.hio)phenyl]-2-morpholino-1 propanone (obtainable under the name Irgacure 907 from Ciba Marienberg GmbH, Bensheim) were homogeneously mixed with stirring.
A viscous LC mass with a greenish gleam is obtained which has the following thermodynamic data:
Glass transition point: 2°C, clearing point: 128°C.
4 g of the LC mass prepared as described above under A) were heated to 70"C and mixed homogeneously, with stirring, with 0.11 g~ of 2-methyl-1-[4-(methyl-thio)phenyl]-2-morpholino-1-propanone (obtainable under the name Irgacure'1'"' 907 from Ciba Marienberg GmbH, Bensheim). The liquid-cryst~~lline material was applied at 80°C using a doctor blade to a polyethylene terephthalate film (Hoechst AG, Films Division, Wiesbaden) in coat thicknesses of 7 micrometers, the film being advanced under the fixed blade at a rate of about 2 meters per minute. The liquid-crystalline molecules are simultaneously oriented owing to the shear gradient between blade and film. This coat was subsequently irradiated for 5 seconds with a mercury discharge lamp (80 watts,/cm) and thus was three-dimensionally crosslinked. 'the coating film produced on the PET film was tack-free and brittle in the hot and the cold state. T_t had a reflection wavelength of 530 nanometers (angle of incidence and viewing angle 45°).
The mechanical separation of the liquid-crystalline material obtained in this way from the substrate was achieved by guiding the film over a deflection roller with a diameter of 10 cm and, in this way, peeling the crosslinked material from the substrate. The grinding of the crosslinked, substrate-free material was carried out in a universal mill. Grinding of the crosslinked polyorganosiloxanes, which werE~ obtained predominantly in the form of leaflets (size: a few millimeters to centimeters), for five minutes gave a pulverulent fraction. The ground material 'was then subjected to a sieving process in order to narrow the particle-size distribution.
E~~le 6: , Preparation of a binder module The following constituents are mixed together thoroughly with stirring:
26.2 parts of a PU dispersion according to DE-A-4 224 617, Preparation Example 3, 8.8 parts of hexamethoxymei~hylmelamine, 5 parts parts of n-butanol, 3.5 parts of a commercial i~hickener based on poly acrylic acid, 0.25 part of N,N-dimethylethanolamine, and 56.25 part of deionized water.
Ex~sle 7:
Preparation of an effect module The following constitue=nts are present in the effect module:
parts parts of the PU dispersion from Example 6, 9 parts of the LCP pigme:at according to Example 30 5 B (particle-size fraction: 1-100 ~tm) , 5 parts of a commercially available aluminum paste which contains 60% of aluminum and is suitable for an aqueous basecoat, 25 parts of butylglycol, 35 1.8 par:.s of the thickener from Example 6, and 0.2 part of N,N-dimethylethanolamine.

The LCP pigments and the aluminum paste are each pasted up with solvents and additives . The binder is then added to the mixture of the two pastes and the ~1892~~

whole is mixed thoroughly. This mixture is then diluted with 22 parts of deionized water.
E~nn 1 a 8 P~enaration of an aaueous effect basecoat 80 parts of the binder module from Example 6 and 20 parts of the effect module from Example 7 were mixed uniformly in order to formulate storage-stable aqueous effect basecoats.
Example 9:
Preparation of a multicoat paint system The aqueous effect basecoat from Example 8 is applied by spraying, in a dry-film thickness of 20 micrometers, to customary, phosphatized metal bodywork panels which have been precoate:d by cathodic deposition and with a black filler. Following the application, the coating is flashed off at room temperature for 10 minutes and then predried at 80°C for 10 minutes. A
commercial two-component polyurethane clearcoat based on acrylate resin is then applied in a dry-film thickness of 50 micrometers, and the resulting paint system is dried at 100°C (panel temperature) for 30 minutes.
A multicoat paint system is obtained which has a bright/dark flop and a strongly pronounced color flop whose color changes from green to blue.

Claims (16)

1. A coating composition suitable as basecoat for multicoat paint systems, comprising:
- one or more customary paint binders, - one or more plateletlike pigments whose color depends on the viewing angle, which consist of oriented, three-dimensionally crosslinked substances of liquid-crystalline structure with a chiral phase, - one or more customary special-effect pigments which differ from said plateletlike, three dimensional crosslinked liquid crystalline pigments.

2. The composition as claimed in claim 1, further comprising at least one of:
- one or more crosslinking agents, - one or more colored absorption pigments - one or more colored absorption fillers, - customary paint additives.

3. The coating composition as claimed in claim 1, which comprises one or more organic solvents.

4. The coating composition as claimed in claim 1, 2 or 3 which comprises water.

5. The coating composition as claimed in claim 1, 2 or 3 wherein one or more customary paint binders selected from the group consisting of polyesters, alkyd resins, polyurethanes, (meth)acrylic copolymers and resins based on cellulose esters are dissolved or dispersed in organic solvents.

6. The coating composition as claimed in claim 4, wherein the customary paint binders are water-dilutable cationically stabilized resins.

7. The coating composition as claimed in claim 6, wherein the cationically stabilized water-dilutable binders are resins which are based on (meth)acrylic copolymers, polyesters, polyurethanes and polyurethaneureas and have a number average molar mass (Mn) of from 500 to 500,000, an OH number of from 0 to 450, an amine number of from 20 to 200 and a glass transition temperature of from -50 to +150°C.

8. The coating composition as. claimed in claim 4, wherein the customary paint binders are water-dilutable anionically stabilised resins.

9. The coating composition as claimed in claim 8, wherein the water-dilutable binders are selected from (meth)acrylic copolymer resins, polyester resins and polyurethane resins having a weight average molar mass (Mw) of from 1000 to 500,000.

10. The coating composition as claimed in any one of the preceding claims, which comprises one or more crosslinking agents based on formaldehyde condensation resins and free or blocked polyisocyanates.

11. The coating composition as claimed in claim 10 wherein the mixing ratio of crosslinking agent to binder resin is from 10:90 to 40:60, based in each case on the weight of solids.

12. The coating composition as claimed in any one of the preceding claims which has a solids content of from to 50% by weight and a ratio of pigment to binder-resin plus any crosslinking agent present plus any paste resin present of form 0.03:1 to 1:1, based on the weight of solids.

13. The coating composition as claimed in any one of the preceding claims, wherein t:he ratio of plateletlike pigment based on three-dimensionally crosslinked substance having a liquid crystalline structure plus special effect pigment to the binder resin plus any crosslinking agent present plus any paste resin present is from 0.03:1 to 0.5:1, based in each case on the weight of solids.

14. The coating composition as claimed in any one of the preceding claims, wherein the volume ratio of plateletlike pigment based on three-dimensionally crosslinked substance having a liquid crystalline structure to the further special effect pigment is from 1:10 to 10:1.

15. A process for the multicoat painting of substrates by applying a basecoat/clearcoat system to an uncoated or precoated substrate, wherein the basecoat applied is a coating composition as claimed in any one of claims 1 to 14.

16. The process as claimed in claim 15, wherein the basecoat is applied to a dark substrate or to a substrate which is coated with a dark coating.