CA2256990A1 - Organic material with metallic luster - Google Patents

Abstract

Flat material comprising at least two uncrosslinked, thermoplastic, cholesteric,liquid-crystalline, main-chain polymers which differ in the pitch of their cholesteric helices, the material reflecting all wavelengths of the visible spectrum and having a mixing gradient of the main-chain polymers which proceeds perpendicularly from the surface of the material.

Description

Description 5 O~ganic ~ t~ l with metallic luster The present invent;on is described in the Gerrnan priority application No. 197 56 974.9, filed December 20, 1997 ~hich is hereby Incorporated by reference as is fully dis- hsecl herein.
The invention relates to polyrners having a metallic luster and to pigments prepared from them, to a prooess for their preparation, and to their use.

Cholen~-~ric liquid~rystaT polymers (cLCP~) are known. ~hey form a hellcal 15 superstructure which results in s~31ective and viewing-angle clependent reflection of light. This reflection effect can be exploited to prepare sp~3ci~' cffect pig.--e,lts (D~ 195 38 700 ~1). The special-effect pigments ale notable not only for a very bright perceived color but also, in particular, for their viewing-angle-dependent color;
in other words, the situation in whlch, for example, an article painted with cholesteric 20 pigments appear~3 green when vi~wed Ytr ight on but blue when viewed at an oblique angle.

rign,e"l~; of this kind whose color is dependent on ~fie~ri"g angle are also obtainable from a crosslinked chol~_te. ic liq~id-crystal polymer (DE 42 40 723 A1).
~5 It is also known that chcl~teric liquid-crystal polymers can be used as a ~olari~dtion device (R. Maurer et al., SID 90 Digest of Technical Papers, Las Vegas 1990, pages 1 1~113). To this end, three liquid-crystalline polymer films whose reflection wavelengths correspond to the three primary colors tred, green and blue), are 30 brought onto one another so as to reflect one polari~alion direction of the incident light over a large section of the visible spectrum, with the result that only the light component ha~ing the opposite polarization direction is transmitted.

1 18. DEZ.1998 11: 15 CL~RI~NT PRT. DEPT. 069 305 81077 NR.062 S.5 EP-A-0 606 ~40 describes a three-cli,.lt:"si~ y cros~linked llquid-crystal film which exhibits a continuously changing twist of the cholesteric helix, so that reflection of one polali~dtio,. direction occurs for all wavel~l,gLl-s of the visible spectrum and only the opposKe component is transmitted. The ~;ontinuously changing twist of the helix is achieved during the crussli,,kin~ reaction by est~blish;ng a conce~ alion gradient of a nematic a~rylate in a cholesteric m~"u",er mixture through the presence of a UV dye~ In another ernbodiment the spontaneous inward diffusion of nonliquid-crystalline polyme, i~le compounds into a cholesteric polyr~er network is used, with conLr~Jlled diffusion to generate a swelling gra~ient, whlGh induces a continuously changing expansion of the cholesteric helix. Both film structur~3s are fixed by means of photnchennically induced addition polymerization. The po~sibility of use as colorants is not mentioned.

2 likewise produces a continuously çhanging twist of the cl,olesteric helix by poly",e,i~dlio,l-incluced diffusion of low molecl~l~r mass compounds from a cholesteric material during a pl~oto.;l,emical polymerization. In this case the change induced in the helix over the layer lhi ~c.,ess is not linear but exponential. This maJces it possible to i"c,~ase the bandwidth of the polarizer ~or a given layer thickness It is also mentioned that at low concentrations (e.g. 1/6) of nonpolymeri~ liquid-crystalline material in the polyrnerizable cholesteric liquid-crystalline material the resulting bandwidth is very greatly r~uce~. Only at relatively high conce,-t-~Lions (e.g., 1/2) are the desired bandwidths obtained. A material of this kind in which lar~e qu~ntities of a compoun~ ~hich cannot be incorporateci by poly",eri ~lion -i.e., which is not bonded covalently to the resulting polymer ne~Nork - are present in a Gholesteric network is uns~it~hle for use as a color pigment. On exposure to the binder which generally co,n~ es organic solvents, there is gw~ of the polymer network and leachin~3 of the constituents ~vhich are not covalently bonde~. It is known th3t following removal of these constituent~ there is volume shrinkage in cholesteric polymer r,ch~.rJ,k (see also A. Stohr, P. Strohrieç~l J. Macrc~n,ol. Soi. -PureAppl.Chem.,A34(7) 1125 (1997):RAM Hikmet B.H.Zwerver.Liquid Crystals 13, 561 (1993)). Consequently, the pitch of the helix falls and the refle~tion I~.DEZ.1998 11: 15 CL~RIRNT P~T.DEPT. 06' ~05 ~1077 NR 06Z 5.6 band shifts to lower ,~ ;hl~ u~ clcngths. Consequently, not all wavelengths of visible light are reflected, and the material appears colored. This characteristic i~
also rossessed by the material from WO 97/16762, so rendering it of no interest for a pigment appl;cation involving metallic luster.

It is an object of the ~,rese-~l invention to provide organic rnaterials havin~ a m~3tallic lus~er, avoiding the disadvantages described above, a simple proCess for their preparation, and possibilities for their use.

10 It has been found that the disadvantages set out in the prior art can be avoided through the use of the~r,~ lic cholesteric liquid~ryxtalline main-chain polymers, it being possible in a simple manner to provide temperature-stable, chemical-resistant and solvent-resistant special-effect pigments having a l1,et~'1ic luster.

15 The pres~nt invention Ihe:r~ provides a flat Illdk~ l comprising at least twouncrosslinked, thermoplastic, chol~st~ric, liquid~rystallinel main-chain polymers which differ in the pitch of their cholesteric helice~, or aj",lJrising at least one ~,,crusslinked, the".,cs~Jla~tic, chr'es~eric, liquid-crystalline, main-chain polyrner and one thermoplastic, nematic polymer, the rll~t~ri~l reflecting all wavelengths of the ;~0 visible spectrum and having a mixin~ gradient of the main-chain polymers which proc0eds perpendicularly from the surface of the material.

By flat t~ateri~l is meant pr~:fer~bly a coat on a support material, or a film or pl-telet 25 The invention also provides a process ~or preparing said flat material, whichcomprises applying at lea~t two th~3r" IU~6Stic, ch,c i e ' aric, liquid crystalline, main-chain polymers which dffler in the pitch of their .;l ,~lest ric helix, or at least one thermopl;~stic chol~ ~eric polymer and a thermopl~-ctic~ nematic polyme~ atop one another on a support substrate and then subjecting the assembly to thermal :~0 conditioning until a metallic effect becornes visible, separ~lin~ the resulting polymer Film, if desired, from the support substrate and ~.ruces~ g it, if desireci, into plRt~let~.

1 18.DEZ.1998 11: 15 CLRRIRNT PRT.DEPT. 069 305 81077 NR.0~Z 5.7 I

In order to ach~eve the effect of the invention it is necessd,y for the cho~teric liquid-crystal polymers that are to be Goated atop one another to have dir~rel ll pitches of the cholesteric helix. This enables polymer molecules of the individual layers to cliffuse into the neighboring layers dLlring the thermal conditioning process 5 and, on the~ basis of these dmerent pitches. to form a helical pitch which changes continuously over the entire layer thickness. When using mor~s than two polymerseach having discrete helical pitches it must be ensured that the polymer~ are coated atop one ar,uther in such a way that within the overall assembly the helical pitch either increases or re~ ces from polymer layer to polymer layer. The number of 10 li~uid~crystal polymers coated atop nne another is arbitrary, but is judiciously from 2 to 7, p~eferably from 2 to 5.

The continuously changing helical pitch obtained after the tllermal conditionin~process can only adopt values between the pKches of the lowermost and topmost 15 cholesteric liquid~;rystal polymer layer.

In order to induce a metaliic luster in the material it is necess~ry for all wavelengths of the visible spectrum to be reflectecl. In general, ll,eref~re, cholesteric liquid~rystal polymer~ with selective reflection in the red or IR spectral range are disposed on one 20 outer face - i.e., the top or bottom - of the material of the invention and cLCPs with selective reflection in the blue or UV spectral range are disposed on the other outer faGe, i.e., the L,ollur" or top. Instead of the red~ 11ectillg or IR reflecting layer it is also posslble to us~ a nematic - that is, untwisted - polymer layer, especially one oon~,oosed of main-chain polymers.
The nematic main-chain polymers (LCPs) employed can be all those LCPs that are known to the sWll~d yvorker, as are set out in G. W. Becker, D. Braun: Kunststo~r-Handbuch [Plastics Handbook]Volume3/3, pages21~-258, Carl HanserVerlag, Munich 19~4. Preferred LC~Ps are those compri~ing monomers from the group of 30 aromatic hydroxycarboxylic acids and/or of aromatic dicarLoxylic acids and aromatic d;ols.

~ 18.DEZ.1998 11:16 CL~RIRNT PRT.DEPT. 069 305 81077 NR.06Z S.8 In the cG"lexl of these ~roups, a~,.h.lic hydroxycarboxylic acids can be replac~cl by cycloaliphatic hydroxycarboxyiic acids or aromatic aminocarboxylic acids, aromatic dic~,L.oxylic ~cids by cycloaliphatic dicdll,oxylic acids, and aromat;c diols byaromat;c dia, ".. Ies, aminophenols and/or ~ycloaliphatic diols.
~:or the stoichic~ elric proportions of these monorners to one another, care should be taken to ensure that the stoichiometry of the functional groups, which is kno~rn to the person skilled in the art, permits polycondensation with the F~,r"l~lion of ester and/or amide linkages.
10 In addition, the~ polymers may also include co,l,ponents having more than ~NOfunctional ~roupsl such as dihydroxybenzoic acids, trihydroxybenzenes or trimellitic acid, for exdrlll,le. These cornponents act as a branching site in the polymer and, in orderto avoid cfosslinking of the ,llaterial, should be added only in small concentrations - for example, fiorn 0 to 5 mol%. Particularly preferred LCPs are15 nematic main-chain polyrners composed of the following units of the individual monomer groups:

Aromatic hydroxycarboxylic acids, aminoca,l~oxylic acid~;

HC~

~ COOH

HOOC:

H~ COOH

! 18.DEZ.1998 11:16 CLRRIRNT PRT.DEPT. 069 305 81077 NR. 06Z S.9 HO ~ COO~

H2N~ COOH

HOOC~=~ COaH

~0 .
Ar~nati~ di~arboxylic acids, aliphatic dicarboxyllc acids:

HOO~COOH

~COOI-I

HOOC

HOOCJ31~COOH

~5 HOOC ~ COOH

CA 02256990 l998-l2-l8 18.DEZ.1998 11:16 CLRRIRNT PRT. DEPT. 069 305 81077 NR. 06Z 5.10 ~CH = CH - COOH
HOOC

HOOC ~CH = CH ~ COOH

Hooc~.3C~3 COOH

5HOO ~
~ ~COO~-I

HOoC~ COOH
N

Alu~ Lic diols, aminophenols, aromat;cdiamines:

CA 02256990 l998-l2-l8 18. DEZ. 1998 11~ i CLRRIRNT PRT. DEPT. 069 305 81077 NR. 0~2 S. 11 H~ OH

H~
5 ~OH

HO~ OH

CS~ /~
H<~(~OH

~OH

OH

H~ ~<

~OH

18. DEZ. 1998 11: 17 ~LRRIRNT PRT. DEPT. 069 305 81077 NR. 0f~Z S. 12 HO~ ( ~OH

O OH

~

H ~ O H

H~H

H2~ NH2 :25 /~\
H2N~oH
~H2 ~2N~

18.DEZ.1998 11:17 CL~RIRNT P~T.DEPT. 069 3~5 81077 NR.06Z S.13 Very particulariy pre~r,~d LCPs are compounds compris;ng p-hydroxybenzolc and/or 2-hyd~oxy~-naF~l,LI~ acid as aron~alic hydroxycarboxylic acid, 2,6-naphthalenedicarboxylic acid, ter~pl~ti.al,c and/or isophthalic acid as aromatic d;carboxylic acid, and hydroquinone, r~sor~i."ol and/or 4,4' clihydroxybiphenyl as 5 aru,.,atic diol.

In a further embodiment of the present invention, at least one of the cholesteric liquid-crystal polymers used on the top or bottom, r~spectively, has a reflection wlor that is with;n the visible spectral range. By this means it is possible to produce 10 metallic effects with, say, a blue or red tinge. The mixing gradient extendin~
perpendicularly from the surface of the ",ate.i~l of the invention is preferably linear, although an exponential ~radient is also possible The mixing gradient which becomes established is correlated with the pitch which changes continuously in the same way; in other words, the mixing gradient co,-es,~oods to a pitch gradient. The 15 respective pitch, in tum, ccjr,~onds to ~he respective ~./clcngth of the r~nect~d light and can be established, in particLll~r, through the selection and/or concentration of a ~NiSting, c~liral component in the m~in-chain polymer.

Cholesteric liquid-crystalline main-chain polymers are generally prepared from a20 chiral component and from hydroxy.;~lL,oxylic acids and/or a combination of dicarboxylic acids and diols. In general, the polymers consist essentially of ..~llldLi~;
co. ,alrL.Ients. It is also p~ssi! I~, however, to employ aliphatic and cycloaliphatic components, such as cyclohexanedic~rL u,~ylic acid, for example.

25 The main~hain polymers employed in accordance with the invention are preferably liquid-crystalline polyesters, polyamides or polyesteramides co~ risi~1g ar~n-~lic and/or cycloaliphatic hydroxycarboxylic acids, ~lUllldLiC aminoGarboxylic acids;..ru,.,alic and/or cycloaliphatic dicarboxylic acids, and aromatic andlor cycloaliphatic diols and/or diamines; and also chiral, bifunctional comonomers.
Preferred cl, ~ le st3~lG polymers for the purpc~ses of the pregent invention are ¦ 18.DEZ.1998 11:17 CLRRI~NT PRT.DEPT. 069 305 81077 NR.06Z 5.14 chols~teric liquid-crystalline main-chain polymers consisting ~sse"Lially of a) from 0 to 99.8 mol% of one or more oo"".ounds from the group of aromatic hydroxycarboxylic acids, cycloaliphatic hydroxycarboxylic acids and ar~matic aminocarboxylic acids;
5 b) from 0 to 50 mol% of one or more compounds from the group of arul"dtic dicarboxylic acids and cycloaliphat;c dic~lboxylic acids;
c) from 0 to 50 rnol% of one or more compounds from the group of aromatic and cycloaliphatic diols and diam;nes;
d~ from 0.1 to ~0 mol%, preferably frorn 1 to 25 mol%, of chiral, bifunctional comorlorners; the overall sum is 100 mol% and the sum of components a), b) and c) is from 60 to 99.~ mol%.

With the percentages indicated care should be taken to observe the stoichiometry, known to the ~ .on skilled in the art, of the functional groups for the polyconde"s~tiol1. In addition, the polymers may also include componentS ha~/ingonly one functional ~roup or having more than two funGtional groups, exar"ples being dihydroxybenzoic acid, trihydroxybenzen~s o~ trimellitic acid. In this way it is possible to exer~ influence on the ~"alec~JI~ weight of the polymers. The components haviny more than ~No fu"~Licj"al groups act as a branchin~ site in the polymer and mu~t only be added in small concerllrclLiorls - for example, from 0 to 5 mol% - if the intention is to avoid crosslinking of the material during condensation.

Particular ~Jr~r~r~llCei5 given to cholesteric main-chain polymers composecl of the followin~ units of the individu~l rlnonomer groups:
25 a) aromatic hyd~oxycarboxylic acids, aminocarboxylic acids; hydroxybenzoic acids, hydroxynaphthalenecal 60xy1ic acids, hydroxybiphenylcarboxylic acids, aminobenzoic acids, hydroxycinnamic acids;
b) ~rullldlic dicarboxylic acids, ~liphatic di~&lboxylic acids:
t~:repllUIaliG acid, isopl~L~ c acid, biphenyldicarboxylic acids, naphthalenedicarboxylic acid~, cyclohexanedicarboxylic acids, pyridinedicarboxylic ~cids, diphenyl ether dicarboxylic acids, c. arboxycinnamic CA 02256990 l998-l2-l8 la.DEZ.1998 11:17 CLRRIRNT PRT. DEPT. ~9 305 81077 NR.062 5.15 acids; and c) aromatic diols, arninophenols, dia,ni"es:
hydroquinone, dihydroxybiphenyls, tetramethyldihydroxybiphenyls, Jhll,alenediols, dihydroxydiphenyl sulfones, dihydroxydiphenyl ethers, dihydroxyterphenyls, dihydroxydiphenyl ketones, phenylenediamines, diarninoanthraquinones, dihydroxyanthraquinone~; and also d) chiral, bifunctional monomers:
isosorbide, isomannide, isoidide, ca",~l,oric acid, (C))- or (L)-methylpiperazine, (D)~ or (L)-3-methyladipic acid, butane-2,~iol and also HO- ~ -OH ~ ~ CX~H

o o an~ ~X~
R~ R R' R' where R and R' are each independently H, C1-C~-alkyl or phenyl, preferably H
or C~3.

The higher the proportion of the twisting chiral component d), the ~reater the twi~liu~
20 and the sr,l~ller the pitch and, consequently, the shbl ler the ~a~clcngth of the l~llected light.

When sulfonic acid ~roups are used as a fu".;tiu"al group for condensation it rnay be advantageous to employ them in an activated fonn: for example, in sulfochloride 25 or sulfonic ester form.

Instead of the substances listed it is also possil~l2 to employ other structural isomers or derivatives of these. Thus it is po~ , for example, to employ aminophenol andtrimellitic anhydride in place of N-(4-hydroxyphenyl)trimellitimide.
The polymer units described rnay also include further substituents, such ~s rTlethyl, CA 02256990 l998-l2-l8 18.DEZ.1998 11:18 CL~RIRNT P~T.DEPT. 0h9 305 81077 NR.062 5.16 n,t:U-oxy, cyano or halo~en, for example.

Very part;cular p-~f~3r~ ce for the purposes of the present invention is given to main-chain poly-~ners wr"~rising one or more monomers from the group p~
5 hydroxyl,ei~, ~;~, 2-hydroxy-6-naplllh i~, terephthalic, isophthalic and 2,6-naphthalenedica.l,oxylic acid~, hydroquinone, reso,~ii"ol and 4,4'~ihydroxybiphenyl, and also camphoric acid, isosorbide, is~ ,al~nide as the chiral component.

10 The polycondensation can be conducted by all conventional methods. An exa,-,ple of a s~:t~le method is the melt condensation u~ith acetic anhydride, as described, for example, in EP-A-0 391 368. The cond~nsation of aGetic anhydride is also possi~le in solution or in disperse or emul~ified phase.

15 The monomers are preferably linked via ester linkages (polyesters), amide linkages (polyesteramide/polyamide) and/or imide linkages (polyesterimide/ p~ ": 'e) but may also be linked by other known types of linkage.

When sel~ lg the monomer ~InitA it must be ensured that the functional~group ~0 stoichiometry, which is known to the person skilled in the art, is ensured, i.e., that functional groups which react with one another in the polycondensation reaction are employed in appropriate molar proportion5. VVhen using dicarboxylic acids and diols, ~or example, the nurnber of hydroxyl groups pre~ent should correspond to the number of GZilbOXyl groups. However, it is also possible to smploy calculated 25 excesses of ful~ctiol~l groups - for example, more carL,oxyl than hydroxyl ~roups - in order, for example, to control the attainable molecul~r ~Iveight in this way.

The carboxylic acid~ can also be r~placed by carboxylic acid derivatives, examples being acid chlorides or c~r6oxylic esters. The hydroxyl components can also be :~0 replaced by co.,~sp~nding hydroxy derivatives, suGh as the acetylated hydroxy Gompol~nds, for exarnple.

CA 02256990 l998-l2-l8 18. DEZ. 1998 11: 18 CLnRIRNT PRT. DEPT. 069 305 81077 NR. 062 5. 17 In order to stabilize the flat materials of the invention, the ci~lesteric liquid-crystalline polymers may also include crosslinkable ~r~ups, 80 making it possible to fix an oriented liquid-crystal polymer by means for example, of photocrosslinking, which preferably takes place following an oper~ r. of extrusion.

In one ~refe,.ed ~It~bu~ ,l the cLCPs are of very low solubili~y, and so their molecular weights cannot be detern~ined by commercially customary methods (GPC, light ~i~Ut- i~ l~). As a measure of the molecular weight it is possible to us~: the intrinsic viscosily of the polymers in a pentafluorophenoUhexafluoroisci~ru~-dnol 10 solution. Particularlysuitable polyrner arethose having an intrinsicviscosit~ of betwecn 0.1 dl/g and 10 dl/g, measure~ at a temperature of 25~C.

The chnleet~-ric liquid~rystal polymers described above can be employed directly for - the purposes of the invention. Alternatively, it is possible to employ ~lends of the 15 cholesteric liquid~crystalline polymers. The blends can, on the one hand, consist of dfflerent cholesteric liquid-crystalline polymers; on the other hand, however, it is also possible to mix the cholesteric liq~id-crystalline polyrners with nematic polymers.

The liquid~rystalline polymers may contain from 0 to 10% by wei~ht, ~r~ferably from ~0 0 to 5% by weight, based on the overall weight, of customary auxili~ries and additives from the gn:lup of flow control additives (e.g., polyacrylate~ or polyesters, as are used in pow~er co~Li..~ systems), stabili~ers (e.g" U\/ or heat stabilizers, ~nliuxi~ants), ~.lti~ and optical brighteners.
Auxiliaries andlor additives are mixed with the cholesteric liquid~rystal polymer until di8tribution is horl ,u~er,eous. Mixing takes place most favorably in the melt of the chD'-steric liquid-cry~tal polymer. Mixing can be carried out using all mixin~
equipment suitable for the purpose, examples beiny dispersion kneading apparatus, ~Banbury kneaders or sc:rew ~ompounders, or by extrusion in, for example. a single-screw or twin-screw extrucler. In the case of extrusion in partiGular it is also 30 r~nssibl~ to 8tart from a pulverulent mixture of the additives with the ~holest~ric liquid-cry~talline polymer.

.

18.DEZ.1998 11:18 CLRRI~NT PRT.DEPT. 069 305 81077 NR.06Z 5.18 The flat material ac~ording to the in~ention wKh metallic luster can be prepared by applying two cholesteric liquid-crystal polymers differing in the pitch of th~3ir chole~l~, io helix to a support substrate, one layer over another, and s~ j e~,1i, lg the assembly to thermal conditioning, thenl if desired, sep~r~Lin~l the liquid-crystalline polymer film from the support s~ t~dla and, if desired, bringing the liquid-~rystalline polymer film into the pl~ t size and platelet form that is appropriate for special-effect pigments.

Cholesteric liquid~rystal polymers dissolved in a solvent can be applied in 10 succes~ n, for e~r.,ple, by knife coating on a planar sul,~ le, such as a sheet, glass plate, paper, or hi~h-temperature-stable pl~stic film or strip or metal foil or strip, the first layer being dried and then the second layer applied and, if desired, the third and ~any additional layers being ap,~l'ed afterthe second layer has been dried.
Altemat~ves to knife coat;ng a~ an ~ 1ic~tioll technique include spraying or rolling.
15 When applying the indi~ridual polymer layers it should be ensured that the overall layer thickl-ess obtained is in the range of 1-100 ,um, preferably be~veen 1 and 2 ,um and, in particular ~ en 3 and 15 ,um. In addition, the thiGkness of the individual layers mLIst be tailored to the number of polymer layers to be applied atop one another.
20 After the last layer has been dried, the polymer flm is heated to the orie, lldliol, ternperature so that as many as pos~ of the helices align ther"selves perpenc~icularly to the sul,sl.~te surface. ~t the orientation temperature, the rnacrol"~le ~es are suflicieuLly mobile for there to be a process of diffusion of macromolecules of a single polymer layer to the over- and underlying layer. With a 25 suitable time for therrnal conditioning, this leads to the devclopment of a helical prtch which changes continuously over the layer as a whole It should be ensured here that the them al conditioning time is obser~red precisely.
Thermal conditioning ~hould be terl,.i.,dted as soon as the metallic effect has been 30 established. Too long a time of thermal conditioning would result in ~ essivedrffusion of the macromolecules and th0 forrnation of a uniforrn pitch over the layer CA 02256990 l998-l2-l8 18. DEZ. 1998 11:19 CLRRInNT PRT. DEPT. 069 305 81077 NR. 06Z 5.19 as a whole. The consequence of this would be that there would be selective rather than broadband reflection of light with. the wavele"ylll corr0sponding to the prevailing average pitch, and the met~3llic efhect would disappear. The tl,e..nal conditioning tirne is generally from 0.1 s to 10 min, preferably from 1 s to 5 min and, 5 in particular from 3 s to ~2 rnin.~ Thermal conditioning generally takes place at a teln,~r~ re be~ocn 100 and 400~C, ~r~f~,dbly between 150 and 300~C, and, in particular, between 180 and 2~0~C.

In one partic. ular embodiment. organic or ~queous disper:.ibn~ of the liquid-10 crystalline polymers are used to prepare the individual polymer layers.

To prepare the polymer l"dt~ri~ls of the invention hav;ng a metallic appear~
particularly ~,r~r~ d process is that in which the metallic efFect is induced throu~h the use of ~Ho cholesteric liquid-crystal polymers which do not reflect in the Yisible 15 sp~cir~l range In this case, one cholesteric liquid-crystal polymerpossesses reflection in the IR range and the other reflection in the UV range. Rec~ ~se of the large differenGe in pitch between the helices. of the two chol~?steric liquid-crystal polymers, a relatively long thern al conditioning time is required in this case in order to induce a continuous pitch ~i~rt:r,ce. This can be of advantage, since it enlarges 20 the ~erlna~ conditionin~ '~indow" and makes the process easier to control. For preparing the polymer of the invention having a metallic appearance one e;3ch of a cl~olesteric liquid-crystal polymerwhich reflects in the IR and, respectively, in the UV
rcgion, a~3 described above, are applied atop one another and thermally conditioned at the orientation temperature for a defined penod. In this arrangement, the IF~- and 25 U\~-reflecting layers can be coated atop qne another directly.

In a particular embodiment, a ch- l~s~eric liquid-crystal polyrner \,vhich reflects in the UV range can also be combined with a ne",~Lic liquid-crystal polymer. This is possible because a c~ole~teric phase Gan be induced from a nematic phase through30 the addition of chiral compol~nds, and nematic and ch~'e teric ph~ses can be mixed.
The nematic compound can also be thought of as a compound of infinite p~ch.

18. DEZ. 1998 11: 19 CLRRIRNT PRT. DEPT. 069 305 81077 NR. 06Z S. Z0 In a preferred ,.,ucess for ,~ ,i"g the material of the invention having a metallic luster, the chlcls~teric liquid-crystal polymers, and additionally a nematic liquid-crystal polymer, are brought atop one anot~r by coextrusion.
If appropriate, a further polymer is coextruded as well, as a support layer.
Suhsequently, the wextrudate is s~je~ted to therrnal conditiol,;"~l as describedabove in order to ge"er~le the metallic efFect.

The orS~;s"ic m~t~rials of the invention having a metallic luster ha~re a brilliant metallic effect which makes them ~l~it~ble ~s starting material for preparing spedal-effect pigments. For this purpose the res~ re liquid-crystal polymers are applied one over the other to a te-r"uL,~LI~r~stable support material - for example, a high-temperature stable plastic strip or film or a metal strip or foil - and are thermally condition~d until the metallic effect is developed. Thereaffer, the polymer layer is separated from the -~upport material and comminuted to the desired platelet sizeusing a size reduction apparatus, It should be ensured that there is always a platelet-shaped geometry - the platelet (r1l~t~1et) diameter should be at least two to three t;mes as biç~ as the platelet thickness; The platelet thickness sholJld lie in the range of 1-100 ~um, preferably b~t veen 1 and Z5 ,um and, in particular, between 3 and 15 l~m. The pl-~el~t di~lneter lies in the range of 10-250 ~m, pr~ferably betwecn 20 and 90 ,um.

Paints comp~isin~ the s~,e~ efrect pigments of the invention can be used to paint natural and synthetic materials, such as wood, metal or glass, especially the bodywork or bodywork parts t~f motor vehicles.
I=or c~hlill~s, p~rticular preference is given to dark substrates. By sul-sL,dle in this context is rneant not only a substrate whose surface has been provided with a dark coat bl t also an inherently dark-colored substrate; for example, a plastics substrate or a met~l substrate that has been coated with a dark oxide layer. Examples of dark 30 co~ts are ~lect.c"~l lurelicall~ applied or spray-applied or powder-applied primer~, plastic primers, surfacer coat~ and ~ lu,lecl,i~. coats, or else solid-color ~asecoats 18. DEZ. 1998 11: 19 CL~RInNT PRT. DEPT. 069 305 81077 NR. 06Z S. Zl and topcoats. Examples of dark suL,stl~tes are dark red, dark blue, dark green, dark brown, dark gray and, in particular, black.
Application of the special-effect pi~ments in the cosmetics sector is a further ~ ssi~ility.
It is also possible to process the m~L~-idl of the invention into ~ oly" ,~r laminates -that is, into flat structures in which two or more layers of material of the invention are separated by one or more light-~s~,Li,ly layers in between.

10 In order to produce an opaque pigment it is nee~ry for the light-al-su, I,i. Iy layer to forrn the center layer of an (at least) three-layer structure. This center layer is covered on either side by one layer of the material of the invention having a metallic luster. Bec~use of the absorbing center layer, a laminate of this kind appears op~ e from both si~es. It is also possible in principle for the laminate to contain 15 more than just two transpar~nt l~yers of the material having a metallic luster. In addition, it may be advanta!3eous to provide the laminate on one or both sides with a transparent clearcoat, which need not be liquid~crystalline.

Suitable clearcoats are, in principle, all known clear~oats or ~ransparent-pigmented 20 coating compositions. In this Gci~ l it is possible to employ both solvent-containing one~,..ponent or ~o-component coating materials and also, preferably, water-thinnable clearcoats and powder coating material~. In some cases it may be jUrtiCio~JS to choose a somewhat thicker clearcoat or to apply two clearcoats cc,r..~,[ i~ing identical or clirr~-~- ,l liquid Glearcoats or transparent powder coating 25 ",ate.ials. As is known, the clearcoat contains further auxiliaries which enhance the surface properties of the coated articles. Mention may be macle, for example, of UV
and light stabilizers, which protect the underlying coats against degradation re~clio~s.

30 The overall layer lhjGI~rIeSS of the laminate of the invention lies in the ~nge from 1 to 100 ~m, pl~f~rdL,ly between 2 and 50 I~m and, in particular, hetween 3 and 15 ~m.

18.DEZ.1998 11:Z0 CL~RIRNT P~T.DEPT. 069 305 81077 NR.06Z S.ZZ

1g D~ g on the clesired arpli~tion, however, layer thicknesses wllich deviate from th;s may also be judicious. It is advantageo~s if the transparent layers having a metallic luster are of comparable thickness. The platelet dia",et~ 3 within the range from 10 to 250 ,um, ~,r~:rt:r~t-ly between 20 and gO ~rn.
The ab~o, L;. ~y interlayer of a polymer laminate need not, ,ecess~rily con~ist of a polymer and need also not consist of or co~ rixe a liquid crystal. It is possible, for example, for the interlayer to consist of a colorant, carbon black, platlslet-shaped particles of graphite, or a c~lar~d polymer. The co"l~.,t of the slJbst~nce which forms 10 the absorbing interlayer in the polymer laminate is judiciously from 1 to 95% by weight, preferably from 3 to 90% by weight.

The color of the laminate can also be influenced by choosing a h~e other than black for the aLso~}~in~ interlayer, such as blue, red or green, for example.
Care should be taken to ensure good adhesion of the absorbing interlayer to the neighboring liquid-crystal polymer layers in o~der to avoid the laminate comin~ apart.
If adhesion is inR~e~ te, the additional illSe~lliGll of high-adhesion interlayers may be jnf'lic'iQlls~ usin~, for example, a polyvinyl acetate layer or other adhesion 20 polymers known to the person skilled in the art.

A process for producing the laminate is desc.i~ed belolv. Two layers in each case of the material of the invention having a metallic luster, prepared as described abov0 and with a maximum layer thickness of 10 ~m, are bonded to a light-absorbing layer.
26 This light-absorbing layer is, for example, a polynler;c adhesive material into which light-~bsorbing particles have been incorporated.

In a further embodiment, the support material for preparing the material of the invention having a metallic luster is itself the light-absorbing layer. Again, a laminate 30 can be produced by double-sided coating.

18.DEZ.1998 11: Z0 CLRRIRNT PRT.DEPT. 069 305 81077 NR.06Z S.Z3 For producing the laminate, particular ~re:r~r~"ee is given to a proGess in which thermoplastic cho'~ ic liquid-crystal polymers in at least four polymer layers and a light-absorbing layer Iying h-tv/~en the second and third layers are coextruded. In this case a sy",l"et,ical layer structure, such as AE3CBA, for example, is pr~fel-e~, 5 where A is a cl,Dl~nic main-chain polymerwith ,~fle~ion the UV range, B is a cholesteric main-chain polymer with reflection in the IR range and C is the li~ht-absorbing layer.
10 If desired, a further polymer is also coextruded, as a support layer.

In a further prefe~ed tmbodi",e"L, two or rnore chol~t~lic liquid-crystalline main-chain polymers with changing cholesteric pitch, as described above f~r c,bLai,~in~ a material having ~etallic luster from solution or from dispersion, are coated atop one 15 a.,~U~er. Subsequently, the light-a~so,l,i-,g layer is applied to the final layer and the cl,~l~ ' ric liquid~rystalline main~hain polymers, in tum, are applied in reverse order to the light-absorbing layer, the second layer being ~r)pliecl after the first layer has been dried and the third and any additional layers being applied, if desired, after the second layer has been dried. In order to develop the continuous change ;n the 20 cholesteric pitch on both sides of th~ light-absorbing layer, as is required for the metallic luster, th;s assembly is subieçt~rl to thermal conditioning at elevatedt~"".e,~t.~re for a certain period.

The np~ e laminates of the in~ention, co",posed of organic ",dte,ials wKh a 25 metallic luster, have a brilliant metallic efFect which makes them suitable as starting material for preparing spec~ ' cffect pigments. Following their product;on, the l~r"i,.ates are comminuted to the desired platelet size using conventional size reduction apparahs. It should be ensured that there is always a platelet-shaped geometry - ~he platelet di~meter should be at least two to three times as big as the 30 platelet thickness. The platelet thickness should lie in the range of 1-100 ,um, preferably beh~een 1 and 25 IJm and, in particular, between 3 and 15 l~m. The plate 18.DEZ.1998 11: 20 CLRRIRNT PRT.DEPT. 0h9 305 81077 NR.062 S.Z4 did,-,~ter lies in the range of 10-250 ,um, preferably b~twccn 20 and 90 ,um.

Paints comprising the spe~;A' cffect pigment-~ of the invention can be used to paint natural and synthetic materials, such as wood, metal or glass, especially the 5 bodywork or bodywork parts of motor vehides. The application of such sreci~l cffect pigments in the cosllleti~s sector i-~ also G~"ceiv~ble.

Consequently, the invention also provides for the use of the flat material having a metallic effect as a spe~i~' cffect pigment and as a colorant in electrophot~,dpl,i~
10 toners and developers, in powder coali-,g materials for triboelectric spraying, and for color filters.

Example A
103 mol of acetic anhydride are added to 30 mol of 2-hydroxy-6-~1a,~)hth~i~ acid, 50 mol of 4-hydroxybenzoic acid, 10 mol of terephthalic acid, 3.5 mol of 4,4'-dihydroxybiphenyl and 5.5 mol of 1,4:3,6-dianhydro-D-sorbitol (isosGr~ide) in a reactor, and a gentl0 sl~d-ll of nitrogen is passed through the mixture. The mixture i8 heated with stirring to 140~C over 1~ minutes and this temperature is maintained for 30 minutes. The temperature is then raised to 325~C over the course of 165 20 minutes, and the melt is stirred at this temperature for 30 minutes more. Acetic acid starts to distill off at about 220~C. Nitrogen flushing is then terrninated, and a vacuum is ~r~plied slowly. The melt is stirred in vacuo (about 5 mbar) for a further 30 minutes The mixture is then aerated with nitrogen, and the polyrner is discharged using an extruder and pelleti7ed.
25 The polymer h~s a bright ~opper color which appears red when viewed o~liquely.
The color appearg as early as during condensation in vacuo and is retained aftercooling.

18. DEZ .1998 11: 21 CLRRI~NT P~T . DEPT . 069 305 81077 NR .062 5.25 Example B
Increasing ~he ~ro,~o, liun of isosorbide to ~%, under otherwise identlcal synthesis conditions, prod~lces a polymer with a golden color whlch appears bluish green when vi~ewec~ obl;quely.

Example C
Increasing the proportion of isoso, I-ide to 6.5%, under otherwise identical synthesis conditions, produces a polymer with a yellowish green color which a~p~ . greenish blue when viewed obliquely.
Example D
Increasing tlle proportion of isosorbide to 7%, under otherwise i.J6"lical synthesis cond;tions, pro~ll-ces a polymerwith a bluish green colorwhich appears blue whenviewed obliquely.
Exarnple E
Ill.;lec~ lg the proportion of isosorbide to 7.5%, under otherwise identical synthesis cor,dilio~s, prod~ces a polymer with a- blue color which appears greenish violet when viewed obliquely.
Example F
Increasin~ the proportion of isoço, L ' I~ to 8.5%, under othenvise identical synthesis conditions, produces a polymer with a reflection wavelen~th in the UV range.

Example G
Using ~3 pn~por~;on of isosorbide of 5%, under otherwise identical synthesis conditions, produces a polymer with ~ reflection wavelength in the IR range.

Example H
103 mol of acetiG anhydride are added to 5 mol of 2-hydroxy-6-naphthoic ac:id, 50 mol of 4-hydroxybenzoic acid, 15 mol of ~,4'-dihydroxybiphenyl and 10 mol of 18.DEZ.1998 11:21 CLRRI~NT PRT.DEPT. 069 305 81077 NR.06Z S.26 camphoric acid in a reactor, and a gentle stream of nitrogen is p~95~3~1 through the mixture. The mixture is heated to 140~C over 15 minutes and this te~penal.lre ismaintained for 30 minutes. The temperature is then raised to 325~C over the course of 165 minutes, and the melt is stirred at thi~ temperature for 30 minutes more.5 Acetic acid starts to distill off at a~out 220~C. Nitrogen flushing is then terrninated and a vacuum is applied slowly. The rnelt ;s stirred in vacuo (about 5 mbar) for a fllrther 30 minutes. The mixture is then aerated with nitrogen, and the polynler is discharged using an extruder and pellet;-en.
The polymer shous reflection in the IR range.
Example I
103 mol ~f acetic anhydride are addecl to 15 mol of 2-hydroxy-6-naphthoic ~3cid, 40 mol of 4-hydroxybenzoic acid, 20 mol of 4,4'-dihydroxybiphenyl and 25 mol of camphoric ac;d in a reactor, and a gentle ~tream of nitrogen is passed through the mixture. The mbcture is heated with stirring to 140JC over 15 minutes and this temperature is maintained for 30 minutes. The temperature i~ then raised to 325~C
overthe wurse of 165 minutes, and the rnelt is stirred at this te",p~,~t-~re for 30 minutes more. Acetic acid st~rts to distill ofF at about ~20~C. ~itrog0n flu~hingl5 then terrninated, and a vacuum is arr'i~ slowly. The melt is stirred in vacuo (about 5 ZO mbar) for a further 30 minuteS. The mixture is then aerated with nitrog~n, and the polymer is di~ch~rged using an extr~der and pelleti7~d.
The polym~r shows reflection in the UV range.

Example 1 ~5 10% by weight di-~ ~.er:.;u.,s of each of the polyme~s from Examples A-E in isobutanol are coated on top of one another in the sequence ~-E on a polyimide film using a 24 ,um handcoater. In this procedure, each individual polymer layer is drie~ ~fter knffe coating and tlle powder ap, ~li~liul, is fixed by drawing the film over a hot surFace at 200UC. After the final polymer ha~ been fixed, the fllm is therrnally conditioned in a~0 convection oven at 220~C for 1 minute. After therrnal conditioning, the polyrner film iLit:j a silvery gray metalliG efFeGt. The overall layer thickness is 11 ,um.

18.DEZ.1998 11:21 CLRRIRNT PRT.DEPT. 069 305 81077 NR.06Z S.Z7 l~xample ~
~0~~ by weight dispersions of each of the polymers fr~m Examples F-G in isobutanol are arlrlie~i using a 24 ,um handcoater to one poly;mide film each, are dried, and are fixed by dr~wing o~er a hot surFace at 200~~, The two films are then placed atop5 one ar,vtl,er so that the two cholesteric liquid~crystal polymers are in col)tact with one anothe~. Subse~lllen~y, the polymers are p~esse~ against one another in a rnelt press at 300UC and 100 bar for 3 seco"~ls.
After pressil ~~1. the polymer film exhibits a s;lvery gray metallic efhect. The overall layer Llli-,hl,ess is 10 I~m.
Example 3 ~!0% by weight dispersions of eac~l of the polymers from Example F and of a commercially available nematic liquld-crystal polymer, such as Vectra~ A950, in isobutanol are applied using a 24 ,um h~ndcoater to one polyimide film each, are15 dried, ~n~ are fixed by drawing over a hot surFace at 200~C. The two films are then placed atop one another so that the cholesteric liquid-~rystal polymer from Example F and the nematic liquid~rystal polymer are in contact with one another.
Subsequently, the polyme~s ~re pressed against one another in a melt press at 300~C and 100 bar for 3 seconds.
20 After pressing, the polymer film exhibits a silvery gray metallic effect. The oYerall layer thickness is 12 I~m.

Example 4 10% by weight dispersioi~s of each of the polymers from Examples A-E in isobutanol 25 are coated on top of one another in the sequence A-E on an aluminum foil using a 24 ,um handcoate~. In this procedure. each inclivi~lal polymer layer is dried after knife coating and the powder ~ ic~Lion is fixed by drawing the foil over a hot surface at 200VC. AKer the final polymer has been fixed, the foil iY thermally conditioned in a convection oven at 220~C for 1 minute. After lh~nn~ ndi~ n;lllg, 30 the polymer film exhibKs a silvery gray metallic effect. ~he overall layer thicknes~ is 11 ,um.

18.DEZ.1998 ll:Zl CLRRIRNT P~T.DEPT. 069 305 81077 NR.06Z S.Z8 To prepare the ~ ci~l cffect pigment, the coated aluminum foil is placed in half-col~enl~dle~ hy.l~u.;l~ ic acid, the alumium support foil dissolvcs and the polynler film .~,r"~i"s. The polymer particles are ground in a universal mill. To narrow the particle size distribution, the milled material is p~se~l through a sieve with ~ mesh 5 size of ~3 ,l~m. The resultant spe~ effect piymçnt is incor,~ur;~kJ into a 2-wrll~Jcillelll cle~ l, sprayed onto a black-primed metal panel, and covered with clearcoat After stoving, the CG~ y exhibits a metallic eflect.

~xample 5 10 20% by weight dispersions of each of the polymers from Exal~plcs H-l in tert-butanolfwater = 1/1 are coated on top of one another on an aluminum foil using a 24 ~um handcoater. In this procedure, each polymer layer is dried after knife coating and the powder application is fKed by .I~ v;,.g the foil over a hot surface at 200~C. After the second polymer has been fixed, the foil is thermally cc~".lilil~ned in a convection 15 oven at 220~C for 1 minute. After thermal conditioning, the polymer film exhibits a silvery gray metallic effect. The overall layer llflr~.l~ss is 10 Lum.
To prepare the sp~ci~ ' cffect pigment, the coated aluminum foil is placed in half-co"c~ l~ h~n~u~l.loric acid, the alumium support foil dissolves and the polymer film remains. The polymer particlss ars ground in ~ un;versal mill. To narrow the 20 particle size distribution, the milled ,--~te,ial is passed throu~h a sieve with a mesh size of 63 um. The resultant spFsc~ ffect pigment is incorporated into a 2~omponent clearcoat, sprayed onto a black-primed metal panel, and covered with clearcoat After stoving, the ccs~lil ,9 exhibits a metallic effect.

25 Example 6 10% by weight dispersions of each of the polymers from Examples A-E in isobutanc~l are co~ted on top o~ one anothe~ irl the sequence A-E on an aluminum foil using a 24 um handcoater. In this procedure, each individual polymer layer is dried after knife coatin~ and the powder application is fixed by drawin~ the foil over a hot30 surface at 200~C. After the final polymer has been flxed, the foil is drawn over a hot metal surface for thermal conditioning. The temperature of the metal surface is 18.DEZ.1998 11:2Z CLRRIRNT PRT.DEPT. 0~9 305 81077 NR.062 5.29 300~C and the contact time of the foil with the metal surface is about 3-10 seconds.
After therrnal ccii ,-litic~"ing, the polymer film exhi~its a silvery gray metallic effect. The overall layer thickness jR 11 ,um.
To prepare the special~ffect pigment, the coated aluminum foil is placed in half-5 conc~entral~d hydrochloric acid, the alunlium support foil dissolves and the polymerfilm remains. The polymer particles are ~round in a universal ~nill. To narrow the particle size distnbution, the milled material is pRs~ed throu~h a sieve with a mesh size of 63 l~m. The resultant .speci~l-effeGt pig"lent is incc,r~ o~l~d into a 2-component clearcoat, sprayed onto a black-primed metal panel, and covered with10 clearcoat. After stovin~, the coating exhibits a I~ dllic effect.

Ex~,.lple 7 The coextrusion plant consists of three single-screw extruders, to which melt pumps are connected. The melt pumps ensure an even, pulse-free flow of the melts. The 15 melt stlt~ "s are brought atop one anothel in the discharge die. Disc~arye is via a slot die. In extruder 1, polystyrene i5 extruded and acts as a support layerto the two outer layer~3. The hNo liquid-crystal main-chain polymers t and G are extn~ded at 280~C; in extruders 2 and 3. The melt streams are conveyed with the same volume ratio. A strip with a width of 20 crn is taken off. The strip has a metalliG color. The 20 liquid~rystal layer is formed very well and has a thickness of from 12 to 15 ,um.
To prepare the spe~:i~' cffect pigment ha\~ing a metallic luster, the strip Is ground in a cutting mill. In the course of ~rinding, the polystyrene i8 detached fr~m the liquid-crystal layer and can be se,.,a,dl~ off subse~Pntly by way of the differences indensity. The liquid~rystal particles are ground in a universal mlll. To narrow the 26 particle size distribution, the ground Illt-blidl is ~ ss~.l through a sieve having a me8h size of 63 ,um. The spe~i~' cffect pigment o~tained is incorporated into a 2~omponent clearcoat, sprayed onto a black-primed metal panel and covered with cle~rcoat. After stoving, the coating exhi~its a metallic effect.

Claims (12)

1) A flat material comprising at least two uncrosslinked, thermoplastic, cholesteric, liquid-crystalline, main-chain polymers which differ in the pitch of their cholesteric helices, or comprising at least one uncrosslinked, thermoplastic, cholesteric, liquid-crystalline, main-chain polymer and one thermoplastic, nematic polymer, the material reflecting all wavelenghts of the visible spectrum and having a mixing gradient of the main-chain polymers which proceeds perpendicularly from the surface of the material.

2) The material as claimed in claim 1, which is a layer on a support material or is a laminate, a film or a platelet.

3) The material as claimed in claim 1 or 2, wherein a cholesteric liquid-crystalline main-chain polymer having selective reflection in the red or IR spectral range is disposed on one outer face of the material and a cholesteric liquid-crystalline main-chain polymer with selective reflection in the blue or UV spectral range is disposed on the other outer face of the material.

4) The material as claimed in one or more of claims 1 to 3, wherein a thermoplastic nematic polymer is arranged on one outer face of the material and a cholesteric liquid-crystalline main-chain polymer with selective reflection in the blue or UV spectral range is arranged on the other outer face of the material,

5) The material as claimed in at least one of claims 1 to 4, wherein the main-chain polymers are polyesters, polyamides or polyesteramides comprising aromatic and/or cycloaliphatic hydroxycarboxylic acids, aromatic aminocarboxylic acids;
aromatic and/or cycloaliphatic dicarboxylic acids, and aromatic and/or cycloaliphatic diols and/or diamines; and also chiral, bifunctional comonomers.

6) The material as claimed in at least one of claims 1 to 6, wherein the main-chain polymers consist essentially of a) from 0 to 99.8 mol% of one or more compounds from the group of aromatic hydroxycarboxylic acids, cycloaliphatic hydroxycarboxylic acids and aromatic aminocarboxylic acids;
b) from 0 to 50 mol% of one or more compounds from the group of aromatic dicarboxylic acids and cycloaliphatic dicarboxylic acids;
c) from 0 to 50 mol% of one or more compounds from the group of aromatic and cycloaliphatic diols and diamines;
d) from 0.1 to 40 mol%, preferably from 1 to 25 mol%, of chiral, bifunctional comonomers; the overall sum is 100 mol% and the sum of components a), b) and c) is from 60 to 99.9 mol%.

7) The material as claimed in claim 6, wherein the chiral, bifunctional monomer is isosorbide, isomannide, isoldide, camphoric acid, (D) or (L)- methylpiperazine, (D)- or (L)-methyladipic acid, butane-2,3-diol and also and where R and R' are each independently H, C1-C8 alkyl or phenyl, preferably H or CH3.

8) The material as claimed in at least one of claims 1 to 7, wherein the main-chain polymer comprises one or more monomers from the group p-hydroxybenzoic, 2-hydroxy-6-naphthoic, terephthalic, isophthalic and 2,6-naphthalenedicarboxylicacids, hydroquinone, resorcinol and 4,4'-dihydroxybiphenyl, and also camphoric acid, isosorbide or isomannide.

9) A process for preparing a material as claimed in one or more of claims 1 to 8, which comprises applying at least two thermoplastic cholesteric, liquid-crystalline, main-chain polymers which differ in the pitch of their cholesteric helix, or at least one thermoplastic cholestetic polymer and a thermoplastic, nematic polymer atop one another on a support substrate and then subjecting the assembly to thermal conditioning until a metallic effect becomes visible, separating the resulting polymer film, if desired, from the support substrate and processing it, if desired, into platelets.

10) The process as claimed in claim 9, wherein more than two main-chain polymers with different pitches of their cholesteric helix are applied atop one another such that the pitch either increases or reduces from polymer layer to polymer layer.

11) The use of a material as claimed in one or more of claims 1 to 8 as a special-effect pigment.

12) The use as claimed in claim 11 as a special-effect pigment for painting natural and synthetic material, especially the bodywork or bodywork parts of motor vehicles, or for cosmetics.