CA2250779A1 - Powder coatings with colour effect depending on viewing angle - Google Patents

Abstract

A powder effect coating with a colour impression depending on the viewing angle, consisting essentially of one or more non-setting cholesteric liquid crystalline polymers or essentially of at least one non-setting nematic and at least one non-setting cholesteric liquid crystalline polymer.

Description

CA 022~0779 1998-09-30 FILE, I~ Tl l'S AI~ENI~E~
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Description Powder coatings whose perceived color depends on the viewing angle The invention relates to powder coatings having a bright perceived color which is dependent on the viewing angle, referred to below as effect powder coating, to processes for their preparation and to their use.

Numerous producers of pigments and coating materials are endeavoring on environmental grounds to replace aqueous paints and coating compositions, and especially those containing solvent, by solvent-free paints and coatings. This has been achieved in particular for unpigmented systems or for systems containing inorganic and/or organic absorption pigments. Replacing the solvent in effect basecoats would be particularly significant, since in order to orient the usually platelet-shaped special-effectpigments these coating materials in the course of processing, as a result of the system, are formulated for low viscosity and therefore have a particularly high solvent content. In connection with the production of effect basecoats, attempts have so far failed to produce solvent-free coatings which meet the performance requirements. Of particular interest in this context are effect coating materials whose coloredness depends on the viewing angle, comprising platelet-shaped cholesteric liquid-crystal pigments as optically active components, as are described, for example, in the following documents: WO95/29961, WO 95/29962, DE 44 18 076 A1, DE 44 18 075 A1, DE 44 16 191 A1 and DE 42 40 743 A1. These applications describe processes in the first step of which platelet-shaped particles are prepared which in the second step are dispersed in aqueous and/or solvent-containing coating systems. In the third step, known processing technologies are used to produce an effect coating therefrom.

DE 44 16 993 A1 describes effect coatings in which the pigment can be applied without binders. However, according to the information in this I CA 022~0779 1998-09-30 document, this is possible only with curable liquid-crystalline polymers using high-boiling solvents. The polymer described in DE-A-44 16 993 is based on 4-hydroxyphenyl 3-hydroxy-2-methylpropyl sulfide as chiral component, whose preparation requires a laborious synthesis. The liquid-crystal polymers are soluble in solvents, with the result that, here too, 5 swelling problems occur with a clearcoat, leading likewise to an alteration of the pitch and thus to a change in the color properties. In addition, the - compounds involved here are not pigments as normally understood by the skilled worker, since they are soluble in numerous solvents. Moreover, the precise establishment of color is difficult with these systems, since it takes 10 place only on the coated surface of the article, and even small differences in temperature lead to marked differences in shade.

The object of the present invention was to develop effect coating systems, and especially effect basecoats, whose processing is simple and requires 15 little or no solvents.

It has been found that powder effect coatings having a perceived color which is dependent on the viewing angle can, surprisingly, consist essentially of one or more cholesteric liquid-crystalline polymers which are 20 not curable.

The present invention provides a powder effect coating having a perceived color which is dependent on the viewing angle, consisting essentially of at least one noncurable cholesteric liquid-crystalline polymer, or essentially of 25 at least one noncurable nematic liquid-crystalline polymer and at least one noncurable cholesteric liquid-crystalline polymer.

The term noncurable is understood as meaning that the polymers concerned are unable to enter, with themselves or with other reactants, 30 into any crosslinking reactions as may take place, for example, as a result of light-induced crosslinking in the case of the cinnamic acid derivatives used in DE-A- 44 16 993.

CA 022~0779 1998-09-30 The present invention relates in particular to powder effect coatings and to processes for their preparation where the effect coat is prepared using no solvents and, in addition, none of the binders that are otherwise customary.

The term effect in the present invention is understood as meaning not only 5 the selective reflections in the visible region that are dependent on the viewing angle, but also selective reflections in the UV and IR regions. The latter selective reflections are not perceptible with the human eye but can easily be determined with the aid of UV and IR spectrometers.

10 The novel powder effect coatings comprise cholesteric liquid-crystalline polymers (cLCPs) which possess a helical superstructure. One consequence of this superstructure is that the material no longer has the anisotropy of the mechanical properties that is customary in the case of nematic liquid-crystal polymers. Another is that the material shows 15 pronounced color effects. These effects are based on the selective reflection of the incident light by the helical superstructure. In this context,the exact reflection color depends on the viewing angle and, in particular, on the pitch of the helix. For any given viewing angle - for example a perpendicular view from above onto a sample - a reflection color appears, 20 which is a color whose wavelength corresponds to the pitch of the helical superstructure. This means that the wavelength of the reflected light is shorter the shorter the pitch of the helix. The helical pitch which develops depends essentially on the proportion of chiral comonomer in the overall composition, on the nature of incorporation into the polymer, on the degree 25 of polymerization and on the structure of the chiral comonomer (helical twisting power). Moreover, many systems still exhibit a more or less pronounced temperature-dependency of the pitch in the cholesteric phase, and thus a variation in the color properties as well. It is readily possible, for example, by varying the proportion of the chiral comonomer, to produce a 30 polymer having a blue, green or gold color effect.

Polymers which can be used as cLCPs in accordance with the invention are all cholesteric liquid-crystalline main-chain polymers and also CA 022~0779 1998-09-30 cholesteric liquid-crystalline side-group polymers or combined main-chain/side-group polymers.

Examples of cholesteric side-group polymers are polysiloxanes, cyclic siloxanes, polyacrylates or polymethacrylates, in noncurable form, having mesogens in the side groups. The mesogens in the side group may include all the structures known to the skilled worker, such as cholesterol-substituted phenylbenzoates or biphenols, for example.

Cholesteric main-chain polymers are generally prepared from a chiral component and from hydroxycarboxylic acids and/or a combination of dicarboxylic acids and diols. In general, the polymers consist essentially of aromatic constituents. However, it is also possible to employ aliphatic and cycloaliphatic components, for example cyclohexanedicarboxylic acid.

In the context of the present invention, preference is given to cholesteric liquid-crystalline main-chain polymers consisting essentially of a) from 0 to 99 mol% of at least one compound from the group consisting of aromatic hydroxycarboxylic acids, cycloaliphatic hydroxycarboxylic acids and aromatic aminocarboxylic acids;
20 b) from 0 to 49.5 mol% of at least one compound from the group consisting of aromatic dicarboxylic acids and cycloaliphatic dicarboxylic acids;
c) from 0 to 49.5 mol% of at least one compound from the group consisting of aromatic diols, cycloaliphatic diols and aromatic diamines;
d) from 1 to 40 mol%, preferably from 2 to 25 mol%, of chiral, bifunctional comonomers;
e) from 0 to 5 mol% of a branchable component having more than two functional groups, 30 the sum adding up to 100 mol%.

In the case of the percentages indicated care should be taken that the stoichiometry of the functional groups for the polycondensation, which is CA 022~0779 1998-09-30 familiar to the skilled worker, is ensured.
In addition, the polymers may also include components having more than two functional groups, for example dihydroxybenzoic acids, trihydroxy-benzenes or trimellitic acid. These components act as a branching site in the polymer and should be added only in low concentrations, for example 5 from O to 5 mol%, in order to avoid crosslinking of the material.

Particular preference is given to cholesteric main-group polymers which are composed of the following units of the individual monomer groups:

10 a) Aromatic hydroxycarboxylic acids, aminocarboxylic acids:

HO ~ , COOH HOOC OH

HO ~ COOH H2N ~ COOH

H O OC /[~o b) Aromatic dicarboxylic acids, aliphatic dicarboxylic acids:

15 HOOC ~ COOH HOOC ~ COOH

HOOC ~ COOH HOOC ~ COOH

~ N ~ CH=CH-COOH
HOOC HOOC ~ CH=CH-COOH

HOOCA~O COOH
~COOH HOOC~ HOOC~

~N ~ COOH
HOOC

c) Aromatic diols, aminophenols, aromatic diamines:
HO
HO~OH ~OH HO~OH

HO~$0H HO~--OH ~OH

HO~[~a~ HO~ ~ HO~C~OH

o O OH

HOJ~ ~ ~OH

H~N~ OH

CA 022~0779 1998-09-30 H,N ~ NH2 ~ NH, d) Chiral, bifunctional monomers:

OH H

HO HOOC~ccooH ~N~,CH3 # # #
HOOC-CH,-CH-CH2-CH2 COOH CH3-CH-CH-CH3 H O O C , . C O O H HOCHZ~ CH2-OH
o o ~X~
R R' R R' in which R and R', each independently, are H, C1-C6-alkyl or phenyl, preferably H or CH3.
Particularly preferred cLCPs are polymers comprising camphoric acid and/or isosorbide as chiral component and also p-hydroxybenzoic acid and/or 2-hydroxy-6-naphthoic and/or terephthalic acid and/or isophthalic acid and/or hydroquinone and/or resorcinol and/or 4,4'-dihydroxybiphenyl 15 and/or 2,6-naphthalenedicarboxylic acid.

The chiral comonomers are preferably employed in an enantiomerically pure form. Where enantiomer mixtures of a comonomer are used, care should be taken to ensure that one enantiomeric form is present in an CA 022~0779 1998-09-30 effective excess.

The monomers employed in accordance with the invention can be used directly or else appropriate precursors can be used, which react under the subsequent reaction conditions to form the desired monomers. For 5 example, aminophenol and trimellitic anhydride can be employed instead of N-(4-hydroxyphenyl)trimellitimide.

Polycondensation can be carried out by way of all of the polycondensation methods known to the skilled worker. A suitable example is the melt condensation with acetic anhydride which is described in EP-A-0 391 368.

The monomers are preferably linked by way of ester linkages (polyesters) and/or by way of amide linkages (polyester amide/polyamide), although linking can also take place via other types of linkage known to the skilled 15 worker, for example polyester imide.

When selecting the monomer units, care should be taken to ensure that the functional groups are in stoichiometry, which is known to the skilled worker; in other words, that functional groups which react with one another 20 in the polycondensation reaction are employed in appropriate proportions.
For example, when using dicarboxylic acids and diols, the number of hydroxyl groups present must correspond to the number of carboxyl groups. In a further embodiment, however, it is possible - in order to vary the molecular weight - to employ monomers from groups b) to d) or the 25 listed components having more than two functional groups in an excess that is required in order to achieve a defined molecular weight. In addition, the molecular weight can be influenced by the use of monofunctional monomers.

30 Instead of the carboxylic acids it is also possible to employ other carboxylic acid derivatives known to the skilled worker, examples being acid chlorides or carboxylic esters. Instead of the hydroxy components, it is also possible to employ corresponding hydroxy derivatives, for example the acetylated .

CA 022~0779 1998-09-30 - hydroxy compounds.

The polymer units described may also contain further substituents, for example methyl, methoxy or halogen.

5 It is also possible to prepare cholesteric liquid-crystalline polymers by mixing colorless and/or colored nematic and/or cholesteric liquid-crystalline polymers. In that case the shade of the powder effect coating can be varied within wide limits and adjusted with precision.

10 Particularly suitable nematic liquid-crystalline polymers are those comprising p-hydroxybenzoic acid and/or 2-hydroxy-6-naphthoic acid;

2,6-naphthalenedicarboxylic acid, terephthalic acid and/or isophthalic acid;
hydroquinone, resorcinol and/or 4,4'-dihydroxybiphenyl.

15 Where main-chain polymers are used the cLCPs possess, in one preferred embodiment, a very low solubility, with the result that their molecular weights cannot be determined by customary methods (GPC, light scattering). As a measure of the molecular weight it is possible to use the intrinsic viscosity of the polymers in a solution of pentafluorophenol/
20 hexafluoroisopropanol. Suitable polymers are those having an intrinsic viscosity of between 0.1 dl/g and 10 dl/g.

The preferred main-chain polymers possess high thermal stability and, as a result of their low solubility, an outstanding stability with respect to the 25 solvents used in coating materials. As a consequence, they render superfluous crosslinking reactions after application to the substrate surface. As a result of this not only the application but also the synthesis is much simpler.

30 The invention also provides a process for preparing a powder effect coating having a perceived color which is dependent on the viewing angle, which comprises converting the noncurable, cholesteric liquid-crystalline polymers and, if desired, the noncurable nematic liquid-crystalline polymers CA 022~0779 1998-09-30 , into a finely divided powder, directly in the course of their synthesis or in a subsequent process, applying this powder to the object that is to be coated, using a powder coating technique, and converting the applied powder by temperature treatment into a film whose perceived color is dependent on the viewing angle.

Where the cLCPs and, where used, LCPs are not obtained in the form of a finely divided powder directly from the synthesis, they must be converted into such a powder after synthesis. Where synthesis is conducted as a melt condensation, then an appropriate first comminution step after the 10 synthesis is extrusion as a strand or strip. The resulting strands or strips can be converted in a known manner, using choppers or granulators, into chips or granules. However, the polymers can also be isolated in other ways and subsequently subjected to coarse comminution by means of cutting and sawing processes.
Further comminution can be appropriately effected using milling equipment of all types and designs. In this context, the ultimate fineness required can be achieved in one process step or else in a number of substeps in identical or different types of mill. If the milling process conducted does not 20 lead directly to the desired minimum fineness and particle-size distribution,then it is appropriate to subject the milled material, during or after the milling process, to sieving or classification procedures in order to guarantee the desired minimum fineness and to obtain a desired, optimum particle-size fraction. Examples of suitable milling apparatus are mills of 25 the vibrating, vibrating-disk, disk, planetary, centrifugal, mortar, ball, cross beater, rotor beater, cutting, hammer, blade, rotor-stator, impact-plate and, in particular, ultracentrifugal, universal, pin and air-jet types. In specific cases, it is also possible to carry out wet milling in ballmills, sandmills, vibrating mills or beadmills.
Milling of the cLPCs and, where used, LCPs can be omitted if they are prepared by polymerization in an emulsified or dispersed phase to give a very finely divided powder.

CA 022~0779 1998-09-30 The novel powder effect coatings can be applied by the following preferred methods:

The polymer powder obtained from the synthesis of the polymer or following a milling procedure is electrostatically charged in the actual 5 spraying process. In the case of the corona process, this is effected by guiding the powder past a charged corona. In this case, the powder itself becomes charged. In the case of the triboelectric or electrokinetic process, the principle of triboelectricity - frictional electricity - is employed. Within the spraying device, the powder acquires an electrostatic charge counter to the 10 charge of the friction partner, generally a hose or a spraying pipe (made of polytetrafluoroethylene, for example). The electrostatic charging leads to a high degree of deposition of the powder on the article that is to be coated.
Following application to the article, the powder coat is heated to temperatures above the softening point of the powder, at which the 15 polymers form a homogeneous film and the helical superstructures are formed. The temperature at which formation of the helical structure begins is referred to below as chiralization temperature.

The specific optical properties of the novel powder effect coatings are not 20 observed until the molecules, above the chiralization temperature of the polymer, form the helical structure. Transition to the cholesteric phase takes place in many cases as early as during the synthesis of the polymers. The wavelength of selective reflection of the cLCPs employed in accordance with the invention is determined by the pitch of the helical 25 structure. The pitch is dependent on the structure of the polymer, on the melt viscosity, on the presence of solvents and, in particular, on the helical twisting power of the chiral monomer. In addition, it is a function of the temperature. Accordingly, the pitch of the helix can also be adjusted by way of the temperature. By cooling the coated substrates rapidly, the pitch 30 of the helix, and thus the selective reflection, can be "frozen in"
permanently. In the case of slow cooling, changes in color properties must be expected. In general, colored substrates are obtained in this way too.
However, it is difficult to determine the final color properties beforehand. If CA 022~0779 1998-09-30 the cooled substrate is heated again, then it is possible to establish new helical pitches, or the same pitches again, and thus to adjust the wavelength of selective reflection. Through this operation the color properties of the coated substrate can be corrected and varied in a simple manner. For practical application it is important that the melting point and 5 the chiralization temperature of the polymer lie above the service temperature of the coated substrate.

.
In addition to temperature and the action of shear forces, the formation of the helical structure can be promoted by means of substrates having 10 polymeric coats, for example polyvinyl alcohol, cellulose derivatives and polyimides. Depending on the structure of the polymers, the orientation of the polymer molecules can also be positively influenced by means of electrical and magnetic fields.

15 A further, preferred possibility for coating articles with pulverulent substances is by flame spraying. In this process the powder is fluidized with a carrier gas (for example in a fluidized bed) and supplied to the central nozle of a flame spraygun. At the same time, in the flame spraygun, a fuel-gas/oxygen mixture is produced which is burnt in 20 numerous small flamelets arranged in an annular configuration around the center. The pulverulent particles then melt and are subsequently deposited on the coating substrate as droplets which, in the course of the spraying process, coalesce to form a film. This technique offers the particular advantage that the melting operation is integrated with the spraying 25 process, so that application of the coating to the article, and film formation, can be done in one operation.

Another preferred embodiment for powder coating is the fluidized-bed sintering technique. For this technique, a fluidized bed is generated in an 30 appropriate container with the aid of a carrier gas and the novel polymer powder. The article to be coated is heated, in a separate thermal chamber, to the temperature required for coating, and after reaching this temperature it is immersed for a certain period in the fluidized bed. In the course of this CA 022~0779 1998-09-30 immersion, pulverulent particles remain adhering to the surface of the article, then melt, coalesce to form a film, and develop the helical structure.
In some cases it is advantageous to subject the coated article to an additional thermal treatment in order to improve film formation and the orientation of the polymer molecules. In other cases the object can be 5 cooled in air or quenched with water. This technique too, offers the particular advantage that the melting operation is integrated with the coating process so that application of the coating to the article, orientation of the polymer molecules and film formation can be done in one operation.

10 In all of the powder coating techniques described, and especially with the fluidized-bed sintering and flame spraying technique, the particle morphology, and thus the flowability of the powder, and also the particle-size distribution of the powder, are of great importance. Preference is given to particles that are as close as possible to spherical and have a narrow 15 size distribution. Spherical particles are obtained readily in processes where polymerization is conducted in an emulsified or dispersed phase.
The milling processes lead - depending on the type of milling employed - to narrower or broader particle-size distributions. In some cases it is advantageous to follow milling by a sieving, classification or screening 20 process in order to obtain a particle-size distribution that is as narrow as possible. In other cases it is advantageous first of all to prepare a very finely divided powder which can subsequently be subjected to controlled agglomeration to give the desired particle size.

25 The desired particle size is critical for the coat thickness of the effect powder coating, the nature of the article to be coated and the application technique employed. If thin coats are desired on the object that is to be coated, then the target mean particle size of the powder is between 1 and 100 ~m, preferably between 15 and 80 ~m. Where thick coats are desired 30 on the article, as are normally applied in fluidized-bed sintering and flame spraying, then a mean particle size of between 80 and 300 ~m, preferably from 100 to 250 ~m, is advantageous. In the case of fluidized-bed sintering and flame spraying it is particularly important to observe the limits on CA 022~0779 l998-09-30 particle size. Excessively small particles are heated too strongly by the high flame temperatures, and become carbonized or are blown away by the flow of gas. Excessively coarse particles, on the other hand, are not melted completely and are unable to undergo optimum orientation in the course of subsequent film formation. In exceptional cases, however, it may also be 5 advantageous to use a particle-size distribution which lies outside this range.

The novel effect powder coatings can be applied to a wide variety of substrates. These substrates may, for example, be articles made from 10 natural and synthetic materials such as, for example, wood, plastics, metal or glass. If the effect coating is applied without a prior coating, then it is advisable to apply it in a coat thickness which masks the substrate. It is of course also possible to apply a plurality of coats or to produce semitransparent coatings. Particular preference is given to coating the 15 bodywork, or bodywork parts, of motor vehicles.

In preferred cases, the effect powder coating is applied to metal or plastics substrates. These have in most cases been coated beforehand. In other words, plastics substrates can be provided with a plastics primer, and 20 metallic substrates generally have an electrophoretically applied primer and, if desired, one or more further coats, for example a filler coat.

Dark substrates are particularly preferred. The term substrate in this context refers not only to a substrate whose surface is given a dark coat 25 but also an inherently dark-colored substrate, for example a plastics substrate or a metal substrate which has been coated with a dark oxide layer. Examples of dark coats are electrophoretically applied, spray-applied or powder-coated primers, plastics primers, filler coats and antistonechip coats, and solid-color basecoats and topcoats. Examples of dark substrate 30 backgrounds are dark red, dark blue, dark green, dark brown, dark gray and, in particular, black. The novel powder coatings can also be applied to light-colored backgrounds or in hiding coats. In that case, however, the viewing-angle-dependent perceived color is expressed only to a weakened CA 022~0779 1998-09-30 extent.

The novel effect powder coatings can be coated with a clearcoat by customary methods. Suitable clearcoats are in principle all known clearcoats or transparent-pigmented coating compositions. In this context it 5 is possible to employ both solvent-containing one-component or two-component coating materials and, preferably, water-dilutable clearcoats and, in particular, powder coatings. In some cases it may be expedient to use a somewhat thicker clearcoat or to apply 2 clearcoats of identical or different liquid clearcoats or transparent powder coatings. As is known, the 10 clearcoat contains further auxiliaries which improve the surface properties of the coated articles. Examples that may be mentioned are UV stabilizers and light stabilizers, which protect the underlying layers against degradation reactions.

15 Prior to or during application, the novel effect powder coatings may have added to them further substances as are customary in the case of plastics processing, painting and coating techniques. Examples that may be mentioned are polymers other than liquid-crystalline polymers, charge control agents, absorption and interference pigments, fillers, adhesion 20 promoters, light stabilizers, other stabilizers, and substances which influence rheology and leveling.

The novel effect powder coatings can be produced with a few, simple process steps, in high yield, and without the production of nonreutilizable 25 waste, and can be applied by all prior-art techniques for powder coating without the use of solvents or otherwise customary binders. In addition to ease of processing, they are notable for high temperature stability, solvent resistance and chemical resistance, and very bright shades with a pronounced dependency of the perceived color on the viewing angle.
In the examples which follow, parts are by weight.

CA 022~0779 1998-09-30 Example A1: Synthesis of a cLCP:

2821 parts of 2-hydroxy-6-naphthoic acid, 6215 parts of 4-hydroxybenzoic acid, 3724 parts of 4,4'-dihydroxybiphenyl and 3203 parts of (R)-(+)-3-methyladipic acid are charged to a reactor,10,460 parts of acetic anhydride are added, and a gentle stream of nitrogen is flushed through.
The mixture is heated to 140~C overthe course of 15 minutes, and this temperature is maintained for 20 minutes. The temperature is then raised to 320~C over the course of 150 minutes, and the melt is held at this temperature for 15 minutes. From about 220~C, acetic acid begins to distill 10 off. The nitrogen flushing is then terminated and reduced pressure is applied. The melt is stirred for a further 30 minutes under reduced pressure (about 5 mbar). The polymer is then subjected to nitrogen, cooled and isolated. When viewed straight on the polymer has a bright golden color, which at an oblique viewing angle appears greenish.
Example A2: Synthesis of a cLCP:

14,110 parts of 2-hydroxy-6-naphthoic acid, 31,077 parts of 4-hydroxybenzoic acid,18,621 parts of 4,4'-dihydroxybiphenyl and 3203 20 parts of (1 R,3S)-(+)-camphoric acid are charged to a reactor, 52,580 parts of acetic anhydride are added, and a gentle stream of nitrogen is flushed through. The mixture is heated to 140~C overthe course of 15 minutes, and this temperature is maintained for 20 minutes. The temperature is then raised to 330~C over the course of 150 minutes, and the melt is held at this 25 temperature for 15 minutes. From about 220~C, acetic acid begins to distill off. The nitrogen flushing is then terminated and reduced pressure is applied. The melt is stirred for a further 30 minutes under reduced pressure (about 5 mbar). The polymer is then subjected to nitrogen, cooled and isolated. When viewed straight on the polymer has a bright golden color, 30 which at an oblique viewing angle appears blue-green.

CA 022~0779 1998-09-30 Example A3: Synthesis of a cLCP:

28,218 parts of 2-hydroxy-6-naphthoic acid, 34,530 parts of 4-hydroxybenzoic acid, 8307 parts of terephthalic acid, 3491 parts of 4,4'-dihydroxybiphenyl and 4567 parts of 1,4:3,6-dianhydro-D-sorbitol 5 (isosorbide) are charged to a reactor, 52,326 parts of acetic anhydride are added, and a gentle stream of nitrogen is flushed through. The mixture is ~ . - heated to 140~C over the course of 15 minutes, and this temperature is maintained for 30 minutes. The temperature is then raised to 335~C over the course of 165 minutes, and the melt is stirred further at this temperature for 30 minutes. From about 220~C, acetic acid begins to distill off. The nitrogen flushing is then temminated and reduced pressure is applied. The melt is stirred for a further 30 minutes under reduced pressure (about 5 mbar). The polymer is then subjected to nitrogen, discharged through an extruder and pelletized.
15 The polymer melts at 180~C and has a bluish green color when viewed straight on. The color develops in the course of condensation under reduced pressure and is retained after cooling.

Example A4: Synthesis of a cLCP:
28,218 parts of 2-hydroxy-6-naphthoic acid, 34,530 parts of 4-hydroxybenzoic acid, 8307 parts of terephthalic acid, 3724 parts of 4,4'-dihydroxybiphenyl and 4384 parts of 1,4:3,6-dianhydro-D-sorbitol (isosorbide) are charged to a reactor, 52,686 parts of acetic anhydride are 25 added, and a gentle stream of nitrogen is flushed through. The mixture is heated to 140~C over the course of 15 minutes, and this temperature is maintained for 30 minutes. The temperature is then raised to 335~C over the course of 165 minutes, and the melt is stirred further at this temperature for 30 minutes. From about 220~C, acetic acid begins to distill 30 off. The nitrogen flushing is then terminated and reduced pressure is applied. The melt is stirred for a further 30 minutes under reduced pressure (about 5 mbar). The polymer is then subjected to nitrogen, discharged through an extruder and pelletized.

CA 022~0779 1998-09-30 The polymer melts at 168~C and has a reddish blue color when viewed straight on. The color develops in the course of condensation under reduced pressure and is retained after cooling.

Example A5: Synthesis of a cLCP:

22,582 parts of 2-hydroxy-6-naphthoic acid, 49,723 parts of 4-hydroxybenzoic acid, 9968 parts of terephthalic acid, 8,714 parts of 1,4:3,6-dianhydro-D-sorbitol (isosorbide) are charged to a reactor, 63,283 parts of acetic anhydride are added, and a gentle stream of nitrogen is flushed through. The mixture is heated to 140~C over the course of 15 minutes, and this temperature is maintained for 30 minutes. The temperature is then raised to 335~C over the course of 165 minutes, and the melt is stirred further at this temperature for 30 minutes. From about 220~C, acetic acid begins to distill off. The nitrogen flushing is then terminated and reduced pressure is applied. The melt is stirred for a further 30 minutes under reduced pressure (about 5 mbar). The polymer is then subjected to nitrogen, discharged through an extruder and pelletized.
The polymer has a dark violet color with a dirty effect. The color develops during condensation under reduced pressure.
Example A6: Synthesis of a cLCP:

45,163 parts of 2-hydroxy-6-naphthoic acid, 38,121 parts of 4-hydroxybenzoic acid, 6977 parts of terephthalic acid, 6,138 parts of 1,4:3,6-dianhydro-D-sorbitol (isosorbide) are charged to a reactor, 63,283 parts of acetic anhydride are added, and a gentle stream of nitrogen is flushed through. The mixture is heated to 140~C over the course of 15 minutes, and this temperature is maintained for 30 minutes. The temperature is then raised to 335~C over the course of 165 minutes, and the melt is stirred further at this temperature for 30 minutes. From about 220~C, acetic acid begins to distill off. The nitrogen flushing is then terminated and reduced pressure is applied. The melt is stirred for a further 30 minutes under reduced pressure (about 5 mbar). The polymer is then CA 022~0779 1998-09-30 subjected to nitrogen, discharged through an extruder and pelletized.
The polymer has a beige color with a slight glimmer. The color develops during condensation under reduced pressure and is retained after cooling.

Example A7: Synthesis of a cLCP:

28,218 parts of 2-hydroxy-6-naphthoic acid, 34,530 parts of 4-hydroxybenzoic acid, 8307 parts of terephthalic acid, 2793 parts of 4,4'-dihydroxybiphenyl and 5115 parts of 1,4:3,6-dianhydro-D-sorbitol (isosorbide) are charged to a reactor, 52,326 parts of acetic anhydride are 10 added, and a gentle stream of nitrogen is flushed through. The mixture is heated to 140~C over the course of 15 minutes, and this temperature is maintained for 30 minutes. The temperature is then raised to 335~C over the course of 165 minutes, and the melt is stirred further at this temperature for 30 minutes. From about 220~C, acetic acid begins to distill 15 off. The nitrogen flushing is then terminated and reduced pressure is applied. The melt is stirred for a further 30 minutes under reduced pressure (about 5 mbar). The polymer is then subjected to nitrogen, discharged through an extruder and pelletized.
The polymer melts at 148~C and has a red-gold color when viewed straight 20 on. The color develops in the course of condensation under reduced pressure and is retained after cooling.

Example A8: Synthesis of a cLCP:

28,218 parts of 2-hydroxy-6-naphthoic acid, 34,530 parts of 4-hydroxybenzoic acid, 8307 parts of terephthalic acid, 2327 parts of 4,4'-dihydroxybiphenyl and 5480 parts of 1,4:3,6-dianhydro-D-sorbitol (isosorbide) are charged to a reactor, 52,326 parts of acetic anhydride are added, and a gentle stream of nitrogen is flushed through. The mixture is heated to 140~C over the course of 15 minutes, and this temperature is maintained for 30 minutes. The temperature is then raised to 335~C over the course of 165 minutes, and the melt is stirred further at this temperature for 30 minutes. From about 220~C, acetic acid begins to distill CA 022~0779 1998-09-30 off. The nitrogen flushing is then terminated and reduced pressure is applied. The melt is stirred for a further 30 minutes under reduced pressure (about 5 mbar). The polymer is then subjected to nitrogen, discharged through an extruder and pelletized.
The polymer melts at 1 58~C and has a green-gold color when viewed 5 straight on. The color develops in the course of condensation under reduced pressure and is retained after cooling.

Example B1: Preparation of a cLCP powder:

10 The pelletized polymer prepared in Example A4 is preground on a cutting mill to a particle size < 2mm. Final milling takes place on a high-performance ultracentrifugal mill with a 0.2 mm sieve separator. This produces a powder having a mean particle size D50 of 69 ~um.

15 Example B2: Preparation of a cLCP powder:

The polymer prepared in Example A3 is preground on a cutting mill to a particle size ~ 2mm. Final milling takes place on an air-jet mill with metering unit. This produces a powder having a mean particle size D50 of 20 31,um.

Example B3: Preparation of a cLCP powder:

The pelletized polymer prepared in Example A4 is preground on a cutting 25 mill to a particle size < 2mm. Final milling takes place with increased throughput on a high-performance ultracentrifugal mill with a 0.2 mm sieve separator. This produces a powder having a mean particle size D50 of 117 ,um.

CA 022~0779 1998-09-30 Example B4: Preparation of a cLCP powder with narrow particle-size fraction:

A vibrating sieve is used to separate off all particles larger than 150 ,um and smaller than 90 ,um from the powder prepared in Example B3, to give 5 a powder having a particle-size fraction of between 90 and 150 ,um.

Example B5: Preparation of an LCP blend:

2000 parts of the cLCP prepared in Example A5 are ground on a cutting mill to a particle size < 2 mm and are mixed with 1000 parts of the cLCP
prepared in Example A6 that has been ground in the same way. The mixture is subsequently extruded in a single-screw extruder at temperatures between 250~C and 320~C to give a strand which is cooled with air and granulated. A blend is obtained which when viewed straight on has a bright blue color.

Example B6: Preparation of a cLCP blend:

Example B5is repeated with a mixture of 15 parts of the cLCP prepared in Example A5 and 15 parts of the cLCP prepared in Example A6.A blend is obtained which when viewed straight on has a bright green-blue color.

Example B7: Preparation of a cLCP powder:

The extruded granules prepared in Example B5 are ground on a universal mill with blade insert to a particle size < 2mm. Final milling takes place with medium throughput on a high-performance ultracentrifugal mill with a 0.2 mm sieve separator. This produces a powder having a particle size of <200 ,um.

CA 022~0779 1998-09-30 Example B8: Preparation of a cLCP powder:

The extruded granules prepared in Example B6 are ground on a universal mill with blade insert to a particle size < 2mm. Final milling takes place with medium throughput on a high-performance ultracentrifugal mill with a 0.2 5 mm sieve separator. This produces a powder having a particle size of < 200 ~m.

.
Example B9: Preparation of a cLCP powder:

10 The polymer prepared in Example A1 is precomminuted to centimeter-sized pieces and is ground on a universal mill with blade insert to a particle size < 1 mm. Final milling takes place with medium throughput on a high-performance ultracentrifugal mill with a 0.2 mm sieve separator. This produces a powder having a particle size of < 200 ,um.
Example B10: Preparation of a cLCP powder:

The polymer prepared in Example A2 is precomminuted to centimeter-sized pieces and is ground on a universal mill with blade insert to a particle 20 size < 2mm. Final milling takes place with medium throughput on a high-performance ultracentrifugal mill with a 0.2 mm sieve separator. This produces a powder having a particle size of < 200 ~m.

Example B11: Preparation of a cLCP powder:
The polymer prepared in Example A3 is ground on a cutting mill to a particle size < 2mm. Final milling takes place on an air-jet mill with metering unit and at high throughput. This produces a powder having a mean particle size D50 ~f 322 I~m.

CA 022~0779 1998-09-30 Example B12: Preparation of a cLCP powder with narrow particle-size fraction:

A vibrating sieve is used to separate off all particles larger than 150 ,um and smaller than 90 ~m from the powder prepared in Example B11, to give 5 a powder having a particle-size fraction of between 90 and 150 lum.

Example B13: Preparation of a cLCP masterbatch:

1470 parts of the cLCP prepared in Example A7 are ground on a cutting 10 mill to a particle size < 1 mm and are mixed with 30 parts of C.l. Pigment Red 149. The mixture is subsequently extruded on a single-screw extruder at temperatures of between 240~C and 290~C to give a strip which is cooled with air and granulated. Granules are obtained which when viewed straight on have a strong red-gold color.
Example B14: Preparation of a cLCP masterbatch:

1470 parts of the cLCP prepared in Example A8 are ground on a cutting mill to a particle size < 1 mm and are mixed with 30 parts of C.l. Pigment 20 Black 7. The mixture is subsequently extruded on a single-screw extruder at temperatures of between 240~C and 290~C to give a strip which is cooled with air and granulated. Granules are obtained which when viewed straight on have a strong green-gold color.

25 Example B15: Preparation of a cLCP powder:

The granules prepared in Example B13 are precomminuted on a cutting mill and ground with a universal mill with blade insert to a particle size < 1 mm. Final milling takes place at medium throughput on a high-30 performance ultracentrifugal mill with a 0.2 mm sieve separator. This givesa powder having a particle size < 200 ,um.

CA 022~0779 1998-09-30 Example B16: Preparation of a cLCP powder:

The granules prepared in Example B14 are precomminuted on a cutting mill and ground with a universal mill with blade insert to a particle size < 1 mm. Final milling takes place at medium throughput on a high-5 performance ultracentrifugal mill with a 0.2 mm sieve separator. This givesa powder having a particle size < 200 ,um.

Example C1:
Preparation of an effect powder coating using a triboelectric spraygun:
The powder prepared in Example B2 is placed in the powder container of the spraying device '~Tribostar" from Intec, Dortmund. The spraying device is fitted with a standard spray pipe and a star-shaped internal rod. This spraying device is used to spray an aluminum panel, primed with a black 15 powder coating, by crosswise application in a spray booth from Intec, Dortmund at a high powder throughput and at a spraying pressure of 3 bar.
For film formation, the coated panel is heated at 275~C for 5 minutes and then dipped in water. A homogeneous film is obtained which when viewed straight on has a bright green-blue color and when viewed at an oblique 20 angle has a bright reddish blue color.

Example C2:
Preparation of an effect powder coating using a corona spraygun:

25 The powder prepared in Example B1 is placed in the powder container of a corona spraygun from Intec, Dortmund. A voltage of 35 kV is applied to the electrodes of the spraygun. This spraying device is used to coat an aluminum panel, which is primed with a black powder coating, by crosswise application in a spray booth from Werner & Pfleiderer, Stuttgart, at medium 30 powder throughput. For film formation, the coated panel is heated at 275~C
for 5 minutes and then dipped in water. A homogeneous film is obtained which when viewed straight on has a bright green-blue color and when viewed at an oblique angle has a bright reddish blue color.

CA 022~0779 1998-09-30 Example C3:
Preparation of an effect powder coating using a flame spraygun:

Some of the powder prepared in Example B12 is placed in the powder container of the flame spraygun ~'Unisprayjet SIJ, fitted with nozzle LTA, 5 from UTP, Bad Krotzingen. The gun is operated at an acetylene pressure of 0.6 bar and an oxygen pressure of 2.5 bar. The powder is sprayed onto a 3 mm thick, sand-blasted steel panel which has been preheated at 280 to 300~C. 60 seconds after the end of application, the panel is dipped into a water bath. A homogeneous, blue-green coating with a thickness of about 10 250 ~Jm is obtained which when viewed at an oblique angle has a red-blue color. If the panel is cooled in air, a film is obtained which when viewed straight on has a green-gold color and when viewed at an oblique angle has a blue-green color.

15 Example C4:
Preparation of an effect powder coating by the fluidized-bed sintering process:

Some of the powder prepared in Example B4 is placed in a fluidized-bed 20 chamber and is fluidized with dry air. A 3 mm thick steel panel which has been heated beforehand to 320~C is immersed in this fluidized bed for 2 seconds. A powder coat is immediately deposited on the suRace of the panel; the coat begins to melt and a blue-green film is formed. Quenching in water gives a film which when viewed straight on is blue-green and when 25 viewed at an oblique angle has a red-blue shade.

Example C5:
Preparation of an effect powder coating using a triboelectric spraygun:

30 The powder prepared in Example B9 is placed in the powder container of the spraying device '~Tribostar" from Intec, Dortmund. The spraying device is fitted with a standard spray pipe and a star-shaped internal rod. This spraying device is used to spray an aluminum panel, primed with a black CA 022~0779 1998-09-30 powder coating, by crosswise application in a spray booth from Intec, Dortmund at a high powder throughput and at a spraying pressure of 3 bar.
For film formation, the coated panel is heated at 275~C for 5 minutes and then dipped in water. A homogeneous film with a thickness of about 25 ,um is obtained which when viewed straight on has a bright reddish gold color 5 and when viewed at an oblique angle has a bright yellow-green color.

Example C6:
Preparation of an effect powder coating using a triboelectric spraygun:

10 The powder prepared in Example B10 is placed in the powder container of the spraying device '~Tribostar" from Intec, Dortmund. The spraying device is fitted with a standard spray pipe and a star-shaped internal rod. This spraying device is used to spray an aluminum panel, primed with a black alkyd/melamine resin stoving enamel, by crosswise application in a spray 15 booth from Intec, Dortmund at a high powder throughput and at a spraying pressure of 3 bar. For film formation, the coated panel is heated at 200~C
for 5 minutes and then dipped in water. A homogeneous film with a thickness of about 25 I~m is obtained which when viewed straight on has a bright reddish gold color and when viewed at an oblique angle has a bright 20 bluish green color.

Example C7:
Preparation of an effect powder coating using a triboelectric spraygun:

25 The powder prepared in Example B10 is placed in the powder container of the spraying device "~g'Tribostar" from Intec, Dortmund. The spraying device is fitted with a standard spray pipe and a star-shaped internal rod. This spraying device is used to spray an aluminum panel, primed with a red alkyd/melamine resin stoving enamel, by crosswise application in a spray 30 booth from Intec, Dortmund at a high powder throughput and at a spraying pressure of 3 bar. For film formation, the coated panel is heated at 200~C
for 5 minutes and then dipped in water. A homogeneous film with a thickness of about 20 ,um is obtained which when viewed straight on has a CA 022~0779 1998-09-30 bright reddish gold color and when viewed at an oblique angle has a bright greenish gold color.

Example C8:
Preparation of an effect powder coating using a triboelectric spraygun:

The powder prepared in Example B10 is placed in the powder container of the spraying device '~Tribostar" from Intec, Dortmund. The spraying device is fitted with a standard spray pipe and a star-shaped intemal rod. This spraying device is used to spray an aluminum panel, primed with a blue 10 powder coating, by crosswise application in a spray booth from Intec, Dortmund at a high powder throughput and at a spraying pressure of 3 bar.
For film formation, the coated panel is heated at 200~C for 5 minutes and then dipped in water. A homogeneous film with a thickness of about 25 ~m is obtained which when viewed straight on has a bright gold color and 15 when viewed at an oblique angle has a bright greenish gold color.

Example C9:
Preparation of an effect powder coating using a triboelectric spraygun:

20 The powder prepared in Example B7 is placed in the powder container of the spraying device '~Tribostar" from Intec, Dortmund. The spraying device is fitted with a standard spray pipe and a star-shaped internal rod. This spraying device is used to spray an aluminum panel, primed with a black powder coating, by crosswise application in a spray booth from Intec, 25 Dortmund at a high powder throughput and at a spraying pressure of 3 bar.
For film formation, the coated panel is heated at 275~C for 5 minutes and then dipped in water. A homogeneous film with a thickness of about 25 ~m is obtained which when viewed straight on has a bright blue color and when viewed at an oblique angle has a bright reddish blue color.

CA 022~0779 1998-09-30 Example C10:
Preparation of an effect powder coating using a triboelectric spraygun:

The powder prepared in Example B8 is placed in the powder container of the spraying device '~Tribostar" from Intec, Dortmund. The spraying device 5 is fitted with a standard spray pipe and a star-shaped intemal rod. This spraying device is used to spray an aluminum panel, primed with a black powder coating, by crosswise application in a spray booth from Intec, Dortmund at a high powder throughput and at a spraying pressure of 3 bar.
For film formation, the coated panel is heated at 275~C for 5 minutes and 10 then dipped in water. A homogeneous film with a thickness of about 25 ,um is obtained which when viewed straight on has a bright green-blue color and when viewed at an oblique angle has a bright reddish blue color. If the effect coating is coated with a customary commercial 2-component polyurethane clearcoat or with a water-dilutable clearcoat, then the 15 brightness of the coating, the selective reflection and the color intensity are intensified.

Example C11:
20 Preparation of an effect powder coating using a triboelectric spraygun:

The powder prepared in Example B2 is placed in the powder container of the spraying device '~Tribostar" from Intec, Dortmund. The spraying device is fitted with a standard spray pipe and a star-shaped internal rod. This 25 spraying device is used to spray a dark red panel of 'g'Ceran glass from Schott, Mainz, by crosswise application in a spray booth from Intec, Dortmund at a high powder throughput and at a spraying pressure of 3 bar.
For film fomlation, the glass panel is heated at 275~C for 5 minutes and then dipped in water. A film is obtained which when viewed straight on has 30 a bright green color and when viewed at an oblique angle has a bright blue color.

CA 022~0779 1998-09-30 Example C12:
Preparation of an effect powder coating using a triboelectric spraygun:

The powder prepared in Example B15 is placed in the powder container of the spraying device "~g'Tribostar" from Intec, Dortmund. The spraying device 5 is fitted with a standard spray pipe and a star-shaped internal rod. This spraying device is used to spray an aluminum panel, primed with a black powder coating, by crosswise application in a spray booth from Intec, Dortmund at a high powder throughput and at a spraying pressure of 3 bar.
For film formation, the coated panel is heated at 275~C for 5 minutes and 10 then dipped in water. A homogeneous film with a thickness of about 30 ~um is obtained which when viewed straight on has a bright red-gold color and when viewed at an oblique angle has a bright greenish gold color with a reddish glimmer.

15 Example C13:
Preparation of an effect powder coating using a triboelectric spraygun:

The powder prepared in Example B16 is placed in the powder container of the spraying device "g'Tribostar" from Intec, Dortmund. The spraying device 20 is fitted with a standard spray pipe and a star-shaped internal rod. This spraying device is used to spray an aluminum panel, primed with a black powder coating, by crosswise application in a spray booth from Intec, Dortmund at a high powder throughput and at a spraying pressure of 3 bar.
For film formation, the coated panel is heated at 275~C for 5 minutes and 25 then dipped in water. A homogeneous film with a thickness of about 20 ,um is obtained which when viewed straight on has a greenish gold color and when viewed at an oblique angle has a bright blue-gold color.

Example C14:
30 Preparation of an effect powder coating by the fluidized-bed sintering process:

Some of the powder prepared in Example B10 is placed in a fluidized-bed CA 022~0779 1998-09-30 chamber and is fluidized with dry air. A wooden board which has been heated beforehand to 220~C is dipped in this fluidized bed for 2 seconds. A
coat is slowly deposited on the surface of the board; this coat begins to melt, and a golden film forms. After heating at 220~C for 5 minutes a film is obtained which is red-gold when viewed straight on and when viewed at an 5 oblique angle has a green-gold color.

Example C15:
Preparation of an effect powder coating using a triboelectric spraygun:

1000 parts of the powder prepared in Example B1 are mixed thoroughly with 1000 parts of the powder prepared in Example B2 and the mixture is placed in the powder container of the spraying device '~Tribostar" from Intec, Dortmund. The spraying device is fitted with a standard spray pipe and a star-shaped internal rod. This spraying device is used to spray an 15 aluminum panel, primed with a black powder coating, by crosswise application in a spray booth from Intec, Dortmund at a high powder throughput and at a spraying pressure of 3 bar. For film formation, the coated panel is heated at 270~C for 5 minutes and then dipped in water. A
homogeneous film with a thickness of about 20 ~m is obtained which when 20 viewed straight on has a greenish blue color and when viewed at an oblique angle has a bright reddish blue color.

Claims (12)

claims:

1. An effect powder coating having a perceived color which is dependent on the viewing angle, consisting essentially of one or more noncurable cholesteric liquid-crystalline polymers, or essentially of at least one noncurable nematic liquid-crystalline polymer and at least one noncurable cholesteric liquid-crystalline polymer, wherein the noncurable cholesteric liquid-crystalline polymer is a cholesteric liquid-crystalline side-group polymer, which comprises polysiloxanes, cyclic siloxanes, polyacrylates and/or polymethacrylates in noncurable form in the main chain and mesogenic groups in the side chains, or a cholesteric liquid-crystalline main-chain polymer, which consists essentially of a) from 0 to 99 mol% of at least one compound from the group consisting of aromatic hydroxycarboxylic acids, cycloaliphatic hydroxycarboxylic acids and aromatic aminocarboxylic acids;
b) from 0 to 49.5 mol% of at least one compound from the group consisting of aromatic dicarboxylic acids and cycloaliphatic dicarboxylic acids;
c) from 0 to 49.5 mol% of at least one compound from the group consisting of aromatic diols, cycloaliphatic diols and aromatic diamines;
d) from 1 to 40 mol% of chiral, bifunctional comonomers; and e) from 0 to 5 mol% of a branchable component having more than 2 functional groups, the sum adding up to 100 mol%, or a combination thereof.

2. An effect powder coating as claimed in claim 1, wherein the chiral bifunctional comonomer comprises one or more compounds of the formulae and in which R and R', each independently of one another are H, C1-C6-alkyl or phenyl.

3. An effect powder coating as claimed in claim 1 or 2, wherein further additives which are not liquid-crystalline are present, from the group consisting of absorption and/or interference pigments, charge control agents, fillers, adhesion promoters, light stabilizers, other stabilizers, and substances which influence rheology and leveling.

4. A process for preparing an effect powder coating as claimed in at least one of claims 1 to 3, which comprises converting the noncurable, cholesteric liquid-crystalline polymers and, if desired, the noncurable nematic liquid-crystalline polymers into a finely divided powder, directly in the course of their synthesis or in a subsequent process, applying this powder to the object that is to be coated, using a powder coating technique, and converting the applied powder by temperature treatment into a film whose perceived color is dependent on the viewing angle.

5. The process as claimed in claim 4, wherein the noncurable cholesteric liquid-crystalline polymers and, if desired, the noncurable nematic liquid-crystalline polymers are prepared in powder form by polymerization in an emulsified or dispersed phase.

6. The process as claimed in claim 4, wherein the noncurable cholesteric and, if used, nematic liquid-crystalline polymers are converted into a finely divided powder after their synthesis by means of a milling process.

7. The process as claimed in one or more of claims 4 to 6, wherein the finely divided powder is applied by means of the corona process, a triboelectric or electrokinetic process, a flame spraying process or a fluidized-bed sintering process to the object that is to be coated.

8. The process as claimed in one or more of claims 4 to 7, wherein the effect powder coating is applied to a dark, preferably black, substrate or primer.

9. The process as claimed in one or more of claims 4 to 8, wherein the effect powder coating is coated with one or more clearcoats.

10. The use of an effect powder coating as claimed in one or more of claims 1 to 3 for coating natural or synthetic materials.

11. The use as claimed in claim 10, wherein the materials to be coated are articles of metal or plastic.

12. The use as claimed in claim 10, wherein the articles to be coated are the bodywork, or bodywork parts, of motor vehicles.