WO1999013019A1

WO1999013019A1 - Method for producing thin films from a non aqueous dispersion and effect pigments with coloring dependent on the angle of observation produced therefrom

Info

Publication number: WO1999013019A1
Application number: PCT/EP1998/005420
Authority: WO
Inventors: Bernd Dewald; Andreas Stohr; Axel Schönfeld
Original assignee: Clariant Gmbh
Priority date: 1997-09-08
Filing date: 1998-08-26
Publication date: 1999-03-18
Also published as: DE19739263A1

Abstract

The invention relates to a method for producing thin films comprised of thermoplastic cholesteric liquid crystal polymers (cLCPs) during which one or more thermoplastic cLCPs are deposited as a non aqueous dispersion on a planar substrate and are heated up to or above the chiralization temperature.

Description

Process for the production of thin films from non-aqueous dispersion and effect pigments made therefrom with coloration which is dependent on the viewing angle

The invention relates to a process for the production of thin films and effect pigments made therefrom from thermoplastic cholesteric liquid crystal polymers (cLCPs) with optically variable properties.

Cholesteric main chain polymers are known and can be prepared analogously to nematic main chain polymers by using an additional chiral comonomer (US-A-4,412,059; EP-A-0 196 785; EP-A-0 608 991; EP-A-0 391 368) or by reacting nematic main chain polymers (LCP) with additional chiral comonomers (EP-A-0 283 273). Cholesteric main chain polymers are characterized by their helical superstructure. On the one hand, this means that the material no longer has the anisotropy of mechanical properties that is customary in nematic liquid crystal polymers. Depending on the content of chiral monomer, the material shows pronounced color effects, which are based on the selective reflection on the helical superstructure. The exact reflection color depends on the viewing angle and above all on the pitch of the helix. For any viewing angle - for example, a vertical view of a specimen - a color with a wavelength that corresponds to the pitch of the helical superstructure appears as the reflection color. This means that the reflected light has a shorter wavelength, the smaller the pitch of the

Helix is. The pitch of the helix that forms essentially depends on the proportion of the chiral comonomer, the type of incorporation into the polymer, the degree of polymerization and the structure of the chiral comonomer. In order to achieve pronounced color effects in the case of thin layers of cholesteric liquid crystals, an absorbent, in particular black, background is generally necessary, since otherwise the non-selective part of the light is reflected on the background due to insufficient coverage of the cholesteric liquid crystals, which weakens the color impression . It is also known (HJ Eberle, Liquid Crystals, 1989, Vol. 5, No. 3, pages 907-916) that other colored substrates can also be used instead of a black substrate.

U.S. Patent 5,364,557 describes a method in which cholesteric

Liquid crystal polymers are knife-coated onto a tape in the melt. After cooling, the thin films are e.g. separated from the belt by scrapers or by ultrasonic treatment and then broken into platelets. The process described has the disadvantage that it can only be used with low-melting polymers with low melt viscosity. Effect pigments based on low-melting cholesteric liquid crystal polymers, however, show insufficient temperature stability in lacquer layers.

EP-A-0 601 483 describes a process by which a polyorganosiloxane is knife-coated and crosslinked at about 120 ° C. on a polyethylene terephthalate film. The mechanical separation of the film obtained from the film is achieved in that the film is guided over a small diameter deflection roller, the crosslinked material peeling off the carrier. This document describes the knife application of a viscous liquid onto a carrier film and subsequent crosslinking to form a thin film. The process is not suitable for converting thermoplastic, solvent-insoluble cholesteric liquid crystal polymers into thin films.

The object of the present invention is to provide a method which avoids the disadvantages listed in the prior art, and to produce pigments dependent on the viewing angle, which have high temperature stability and high chemical resistance (insolubility).

It has been found that, surprisingly, this object can be achieved by applying a non-aqueous dispersion of a thermoplastic, cholesteric liquid-crystalline polymer to a planar substrate.

The present invention relates to a method for producing thin films of thermoplastic cholesteric liquid-crystalline polymers, characterized in that one or more thermoplastic cholesteric liquid-crystalline polymers are applied as a non-aqueous dispersion to a planar substrate and heated to or above the chiralization temperature.

In the process according to the invention, normally ground, in a preferred embodiment additionally sifted, polymer particles are dispersed in organic solvents and applied to a planar substrate with the desired layer thickness. After the applied dispersion has dried, the polymer layer is heated to or above the chiralization temperature.

Organic solvents, in particular aliphatic hydrocarbons, such as hexane, heptane, cyclohexane, terpenes, liquid paraffins, oils, come as non-aqueous liquids which serve as the dispersion medium for the finely divided polymer particles; aromatic hydrocarbons, such as benzene, toluene,

Xylene; Alcohols such as methanol, ethanol, isopropanol, butanol, octanol; Esters such as ethyl acetate, butyl acetate, amyl acetate, dioctyl phthalate; halogenated hydrocarbons such as chloroform, methylene chloride, perchlorethylene, trichlorethylene, chlorobenzene; Ketones such as methyl isobutyl ketone, methyl ethyl ketone, acetone, cyclohexanone, isophorone; and liquid polyhydroxy alcohols, such as

Ethylene glycol, propylene glycol, glycerin and polyethylene glycol are considered. In addition, other additives, in particular dispersing additives and thickeners, such as, for example, polyether compounds, as described in EP 0 359 034 B1, or organically soluble cellulose ethers or fatty acid alkanolamides can be used to prepare non-aqueous dispersions.

With the added amounts, care must be taken that the color impression and the color flop are not impaired.

The added amounts of the other additives are between 0 to 5% by weight, in particular between 0.01 to 3% by weight, based on the total amount of the dispersion.

The non-aqueous dispersion can be prepared using all known dispersing and homogenizing units which are suitable for this purpose. Examples include dissolvers, Ultraturrax and agitator ball mills.

It is advantageous to grind the polymers obtained in the synthesis as coarse-grained material. For example, ultracentrifugal mills, pin mills or air jet mills can be used. It is also advantageous to adjust the regrind to a suitable grain size and grain size distribution by sifting. The aim is ad ₅₀ value less than 30 μm, preferably less than 15 μm, in particular less than 10 μm.

It is advantageous if the non-aqueous dispersion contains the thermoplastic cholesteric liquid crystal polymer in an amount of 5 to 60% by weight, in particular 10 to 50% by weight, based on the total weight of the dispersion.

In a preferred process, the ground and sifted cholesteric liquid crystal polymer is dissolved in an organic solvent using a dissolver or Ultraturrax, optionally with the addition of a dispersing additive dispersed. The dispersion is then applied to the carrier substrate using a doctor blade, dried and heated to the chiralization temperature.

Applying the non-aqueous dispersion and adjusting the

The layer thickness can be achieved not only by varying the doctor blade gap, but also via the concentration of the dispersion. However, the layer thickness can also be adjusted using an air brush. Other methods of applying the non-aqueous dispersion to the substrate may also be mentioned, such as spraying, printing or rolling.

In a special embodiment, the substrate is coated not only on one side but on both sides. This is particularly interesting if the carrier substrate is to remain in the effect pigment, e.g. transparent particles (thin glass plates) or opaque particles, or a separation of the cLCP from the substrate on both sides is possible, e.g. by dissolving the

Substrate layer.

The thickness of the polymer layer after drying is normally between 1 and 100 μm, preferably between 1 and 25 μm, in particular between 3 and 15 μm.

All temperature-stable materials are suitable as planar carrier substrates for the process according to the invention. Temperature-stable polymer films or strips, metal foils or strips and glass plates or strips are preferably used. Polyimide films, cellulose films and

Aluminum foils.

For the metal foils, both pure metal foils and laminated metal foils can be used.

It can be advantageous if the surface profile of the polymer films is supported by leveling additives in order to obtain smooth surfaces and the To prevent the formation of craters and "fish eyes". Examples of suitable ones

Leveling additives are polyacrylates and polyesters, some of which are based on

Silicon dioxide can be adsorbed, as in conventional

Powder coating systems are used.

It is particularly advantageous to follow the surface course of the polymer film

Support rollers. For this purpose, the dried dispersion application with a

Foil covered and rolled at the chiralization temperature.

The polymer films are preferably still removed after the cover film has been removed

Chiralization temperature annealed.

All temperature-resistant polymer films or strips, as well as metal foils or strips, which may also have special coatings, are suitable as cover films for the rolling process. Polyimide foils and silicone-coated aluminum foils are preferred.

The formation of the helical structure can also be promoted by substrates with polymeric layers, such as, for example, polyvinyl alcohol, cellulose derivatives or polyimides. Depending on the structure, the orientation process of the polymer molecules can be positively influenced by electrical and magnetic fields.

The thermoplastic cholesteric polymers which can be used according to the invention include both cholesteric liquid-crystalline main chain polymers, cholesteric liquid-crystalline side group polymers and combined liquid-crystalline main chain / side group polymers.

Cholesteric liquid-crystalline side group polymers are, for example, polysiloxanes, cyclic siloxanes, polyacrylates or polymethacrylates with mesogens in the side groups. The mesogens in the side group are, for example, phenylbenzoates or biphenols substituted with cholesterol. The main chain polymers are preferably liquid-crystalline polyesters, polyamides or polyesteramides, the aromatic and / or cycloaliphatic hydroxycarboxylic acids, aromatic aminocarboxylic acids; aromatic and / or cycloaliphatic dicarboxylic acids, and aromatic and / or cycloaliphatic diols and / or diamines; as well as chiral, bifunctional comonomers.

Cholesteric liquid-crystalline main chain polymers are generally produced from a chiral component and from hydroxycarboxylic acids and / or a combination of dicarboxylic acids and diols. As a rule, the polymers consist essentially of aromatic constituents. However, it is also possible to use aliphatic and cycloaliphatic components, such as, for example, cyclohexanedicarboxylic acid.

Preferred cholesteric polymers for the purposes of the present invention are cholesteric liquid-crystalline main chain polymers consisting essentially of a) 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) 0 to 50 mol% of one or more compounds from the group of aromatic dicarboxylic acids and cycloaliphatic dicarboxylic acids; c) 0 to 50 mol% of one or more compounds from the group of aromatic and cycloaliphatic diols and diamines; d) 0.1 to 40 mol%, preferably 1 to 25 mol%, of chiral, bifunctional

Comonomers; the total sum being 100 mol% and the sum of a), b) and c) being 60 to 99.9 mol%.

With the percentages given, care must be taken to ensure that the stoichiometry of the functional groups known to the person skilled in the art

Polycondensation is guaranteed. In addition, the polymers can Contain components with only one functional group or with more than two functional groups, such as dihydroxybenzoic acid, trihydroxybenzenes or trimellitic acid. In this way, the molecular weight of the polymers can be influenced. The components with more than two functional groups act as a branching point in the

Polymer and may only be added in small concentrations, for example 0 to 5 mol%, if crosslinking of the material is to be avoided during the condensation.

Cholesteric main chain polymers which are built up from the following building blocks of the individual monomer groups are particularly preferred:

a) Aromatic hydroxycarboxylic acids, aminocarboxylic acids: hydroxybenzoic acids, hydroxynaphthalenecarboxylic acids, hydroxybiphenylcarboxylic acids, aminobenzoic acids, hydroxycinnamic acids

b) Aromatic dicarboxylic acids, aliphatic dicarboxylic acids, erephthalic acid, isophthalic acid, biphenyldicarboxylic acids, naphthalenedicarboxylic acids, cyclohexanedicarboxylic acids, pyridinedicarboxylic acids, diphenylether dicarboxylic acids, carboxycinnamic acids and

c) aromatic diols, aminophenols, diamines: hydroquinones, dihydroxybiphenyls, tetramethyldihydroxybiphenyls, naphthalenediols, dihydroxydiphenylsulfones, diihydroxydiphenyl ethers, dihydroxyterphenyls,

Dihydroxydiphenyl ketones, phenylenediamines, diaminoanthraquinones, dihydroxyanthraquinones and

d) Chiral, bifunctional monomers: isosorbide, isomannide, isoidide, camphoric acid, (D) - or (L) - methylpiperazine, (D) - or (L) - 3-

Methyl adipic acid, butane-2,3-diol,

wherein R and R 'are each independently H, C ^ Ce alkyl or phenyl, preferably H or CH ₃ .

When using sulfonic acid groups as a functional group for condensation, it may be advantageous to use them in an activated form, for example as sulfochloride or as sulfonic acid ester.

Instead of the substances listed, other structural isomers or derivatives of these can also be used. For example, it is possible to use aminophenol and trimellitic anhydride instead of N- (4-hydroxyphenyl) trimellitimide.

The polymer building blocks described can also contain further substituents, such as, for example, methyl, methoxy, cyano or halogen.

For the purposes of the present invention, very particular preference is given to polymers containing one or more monomers from the group p-hydroxybenzoic acid, 2-hydroxy-6-naphthoic acid, terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, hydroquinone, resorcinol and 4,4'- Dihydroxybiphenyl and camphoric acid, isosorbide or isomannide as chiral component.

The polycondensation can be carried out by all customary methods. For example, melt condensation with acetic anhydride, which is described, for example, in EP-A-0 391 368, is suitable. Condensation with acetic anhydride is also possible in solution or in the disperse or emulsified phase. The monomers are preferably linked via ester bonds (polyester), amide bonds (polyesteramide / polyamide) and / or via imide bonds (polyesterimide / polyimide), but the linkage can also take place via other known types of linkage.

When selecting the monomer units, care must be taken to ensure that the stoichiometry of the functional groups known to the person skilled in the art is ensured, i. H. that functional groups that react with one another in the polycondensation reaction are used in appropriate molar ratios. For example, when using dicarboxylic acids and diols, one of the

Number of carboxyl groups corresponding number of hydroxyl groups be present. However, targeted excesses of functional groups, for example more carboxy groups than hydroxyl groups, can also be used in order to control the achievable molecular weight, for example.

Instead of the carboxylic acids, carboxylic acid derivatives such as acid chlorides or carboxylic acid esters can also be used. Instead of the hydroxy components, corresponding hydroxy derivatives, such as, for example, the acetylated hydroxy compounds, can also be used.

The cholesteric liquid-crystalline polymers can also contain crosslinkable groups, so that it is possible to fix an oriented liquid-crystal polymer by, for example, photo-crosslinking, which preferably takes place after extrusion.

In a preferred embodiment, the cLCPs have a very low solubility, so that their molecular weights cannot be determined using commercially customary methods (GPC, light scattering). The intrinsic viscosity of the polymers in a solution of pentafluorophenol / hexafluoroisopropanol can be used as a measure of the molecular weight. Are suitable Polymers with an intrinsic viscosity between 0.1 dl / g and 10 dl / g at a temperature of 25 ° C.

The cholesteric liquid crystal polymers described above can be used directly in the context of the invention. However, it is also possible to produce thermoplastic blends from the cholesteric liquid-crystalline polymers. The blends can either consist of various thermoplastic cholesteric liquid-crystalline polymers, but it is also possible to mix the cholesteric liquid-crystalline polymers with cholesteric or nematic polymers.

It is also possible to mix the thermoplastic cholesteric polymers with colorants, it being possible to achieve special coloristic effects. Colorants are understood here to mean both pigments and dyes. The pigments can be inorganic or organic in nature. Examples of inorganic pigments are: titanium dioxide, iron oxides, mixed metal oxide pigments, cadmium sulfides, ultramarine blue or chromate molybdate pigments. As organic pigments, all can be known to the person skilled in the art from the relevant literature, e.g. W. Herbst, K. Hunger, Industrial Organic Pigments, VCH Verlag, 1987, well-known pigments are used, e.g. Carbon black, anthanthrone, dioxazine, phthalocyanine, quinacridone, diketopyrrolopyrrole, perylene, perinone, azomethine, isoindoline or azo pigments. Suitable dyes are, for example, quinophthalene, perinone, anthraquinone, azomethine complex, azlactone and azo dyes. The dyes can be completely or partially dissolved in the cholesteric liquid crystal polymer.

In order to achieve special coloristic effects, mixtures of different pigments or dyes or mixtures of dyes with pigments can also be used as colorants. The quantitative ratios between the cholesteric liquid-crystalline polymer and the colorant can vary within wide limits and depend on the type of colorant and the desired color effect. In general, the colored polymer contains 0.1 to 10% by weight of colorant. Furthermore, 0 to 10 wt .-%, preferably 0 to 5 wt .-%, based on the total weight, of leveling additives (e.g. polyacrylates, polyesters), stabilizers (e.g. UV or heat stabilizers, antioxidants), antistatic agents and optical brighteners in the cholesteric liquid crystal polymer may be included.

Colorants and / or auxiliaries and additives are mixed with the cholesteric liquid crystal polymer until a homogeneous distribution is obtained. Mixing is most advantageously carried out in the melt of the cholesteric liquid crystal polymer. Mixing can be carried out with all suitable mixing units, such as dispersion kneaders, © Banbury kneaders or screw kneaders, or by extrusion. In the case of extrusion in particular, a powdery mixture of the additives with the cholesteric liquid-crystalline polymer can also be assumed.

The colorant can also be added directly during the preparation of the cholesteric liquid-crystalline polymer, advantageously towards the end of the polycondensation reaction, preferably immediately before the finished polymer is discharged.

It is also possible to incorporate the colorant into the cholesteric liquid crystal polymer in the form of a master batch. Synthetic and natural waxes, polymers and rubbers can be used as carriers for a masterbatch. However, the preferred carrier for a masterbatch is the cholesteric liquid crystal polymer itself. The masterbatch can contain a pigment or a dye or else a mixture of different pigments and / or dyes. You can also add more to the masterbatch Auxiliaries and / or additives are incorporated. Such masterbatches can be produced by all known processes, for example by intimately mixing the colorants with the carrier in the melt in suitable mixing units, for example dispersion kneaders, Banbury kneaders or screw kneaders, for example twin-screw kneaders. The cholesteric liquid-crystalline polymer can be colored with the masterbatch by mixing the two materials and then extruding them. The masterbatch can also be metered in as a melt into the melt of the cholesteric liquid crystal polymer via a side extruder and / or a melt pump. The most economical way to do this is with

Discharge of the cholesteric liquid crystalline polymer from the reactor after the polycondensation.

The colored liquid-crystalline polymers produced by the processes described above are normally in the form of a physical mixture

Colorant and polymer before. Since the manufacturing process generally also works at higher temperatures, it cannot be ruled out that in the case of colorants with functional groups such as carboxyl, sulfo or hydroxyl, a chemical bond to the cholesteric liquid-crystalline polymer takes place at least in part.

The present invention also relates to a process for the production of effect pigments, characterized in that, as described above, one or more thermoplastic cholesteric liquid-crystal polymers are processed as non-aqueous dispersion on a planar support substrate to give thin films, and then the liquid-crystalline polymer films are separated from the support substrate and the polymer films are brought into the platelet size and shape suitable for effect pigments.

The thermoplastic cholesteric suitable for effect pigments

Liquid crystal polymers are themselves unsuitable to use them according to the conventional processes, such as bubble extrusion or flat film extrusion, to produce thin films. The special optical properties of the cholesteric liquid crystal polymers are only observed when the molecules form the helical structure at or above the chiralization temperature of the polymer. For optimal and rapid formation of the helix, the thermoplastic cholesteric liquid crystal polymers are therefore preferably processed into thin films at temperatures which are above the chiralization temperature and thus significantly above their melting temperatures. The wavelength of the selective reflection of the cholesteric liquid crystal polymers used is determined by the pitch of the helical structure.

The pitch depends on the structure of the polymer, the melt viscosity, the presence of solvents and in particular on the twisting power of the chiral monomer ("helical twisting power"). It is also a function of the temperature.

To produce platelet-shaped effect pigments from the cholesteric liquid-crystal polymers, the polymer film obtained according to the invention is separated from the carrier substrate. When using a polymer film as the base, the mechanical separation of the brittle cholesteric liquid crystal polymer from the base can e.g. in that the

Underlay is guided over a pulley with a small diameter. This causes the liquid crystal polymer to peel off the carrier film. The flaking can be improved by using a liquid jet or by treatment in an ultrasonic bath. Any other method with which the liquid-crystalline polymer can be removed from the base is, however, also suitable.

In a further embodiment, the substrate is coated with a release layer which, as an intermediate layer between the cLCP and the substrate, facilitates the detachment of the cLCP from the substrate. A thin layer of a polymer that is soluble in water or in an organic solvent can serve as the release layer. It is about ensure that the melting and flow properties of the release layer polymers are matched to the chiralization temperature of the cLCP. Care must also be taken to ensure that the release layer is not destroyed when the non-aqueous dispersion is applied. Water-soluble polymers are homo- and copolymers with water-soluble ones

Groups, e.g. Polyvinyl alcohol, polyester sizing, homo- and copolymers of vinyl pyrrolidone, homo- and copolymers of acrylic acid or cellulose derivatives. Organically soluble polymers are e.g. Polyphenylene oxide, cycloolefinic copolymers, polymethyl methacrylate and polycarbonates. In a further embodiment, the carrier material is dissolved. In the case of a metal foil as the carrier material, preferably made of aluminum, the liquid-crystalline polymer film can be separated from the carrier foil by passing the tape into an acid or base bath after the baking process, the metal dissolving.

The liquid crystalline polymer flakes obtained can be brought to the desired particle size by grinding and / or sieving, a platelet-shaped geometry should be obtained, i.e. a platelet diameter that is at least twice, preferably at least three times, the platelet thickness.

In order to obtain an optimal color impression through selective reflection, the effect pigments must have a flat shape as flat as possible. The thickness of such flake-like effect pigments is generally between 1 μm and 100 μm, preferably between 1 μm and 25 μm and in particular between 3 μm and 15 μm. Depending on the desired application, deviating layer thicknesses can also be appropriate.

Effect pigments with a color impression depending on the viewing angle can be used for coloring paints, cosmetics and as printing pigments, for example for security printing or decorative packaging printing. Paints which contain the effect pigments according to the invention can be used for painting natural and synthetic materials, for example wood, metal or glass, in particular the body or body parts of motor vehicles.

Examples of thermoplastic cholesteric liquid crystal polymers

Example A

17 mol of 2-hydroxy-6-naphthoic acid, 50 mol of 4-hydroxy-benzoic acid, 20 mol of 4,4'-dihydroxybiphenyl and 13 mol of camphoric acid are mixed in a reactor

103 moles of acetic anhydride were added and flushed through with a gentle stream of nitrogen. The mixture is heated to 140 ° C. with stirring in the course of 15 minutes and this temperature is maintained for 30 minutes. The temperature is then raised to 325 ° C. in the course of 165 minutes and the melt is stirred further at this temperature for 30 minutes. Acetic acid begins to distill off at approx. 220 ° C. The nitrogen purge is then stopped and a vacuum is slowly applied. The melt is stirred for a further 30 minutes under vacuum (approx. 5 mbar). It is then aerated with nitrogen and the polymer is discharged and pelletized using an extruder. The polymer has a brilliant, reddish-yellow color that appears bluish green when viewed at an angle. The color already appears during the condensation in a vacuum and is retained after cooling.

Example B 30 moles of 2-hydroxy-6-naphthoic acid, 50 moles of 4-hydroxy-benzoic acid, 10 moles

Terephthalic acid, 2 moles of 4,4'-dihydroxybiphenyl and 8 moles of 1,4: 3,6-dianhydro-D-sorbitol (isosorbide) are mixed in a reactor with 103 moles of acetic anhydride and flushed through with a gentle stream of nitrogen. The mixture is heated to 140 ° C. with stirring in the course of 15 minutes and this temperature is maintained for 30 minutes. The temperature is then raised to 325 ° C. in the course of 165 minutes and the melt continues at this temperature for 30 minutes touched. Acetic acid begins to distill off at approx. 220 ° C. The nitrogen purge is then stopped and a vacuum is slowly applied. The melt is used for more

Stirred for 30 minutes under vacuum (approx. 5 mbar). It is then aerated with nitrogen and the polymer is discharged and pelletized using an extruder.

The polymer has a brilliant, yellow color that appears bluish green when viewed at an angle. The color already appears during the condensation in a vacuum and is retained after cooling.

Example C

18 mol of 2-hydroxy-6-naphthoic acid, 48 mol of 4-hydroxy-benzoic acid, 17 mol of 4,4'-dihydroxybiphenyl and 17 mol of camphoric acid are mixed in a reactor with 103 mol of acetic anhydride and flushed through with a gentle stream of nitrogen. The mixture is heated to 140 ° C. with stirring in the course of 15 minutes and this temperature is maintained for 30 minutes. After that the

Temperature increased to 325 ° C within 165 minutes and the melt was further stirred at this temperature for 30 minutes. Acetic acid begins to distill off at approx. 220 ° C. The nitrogen purge is then stopped and a vacuum is slowly applied. The melt is stirred for a further 30 minutes under vacuum (approx. 5 mbar). Then it is aerated with nitrogen and the polymer with a

Extruder discharged and pelletized.

The polymer has a brilliant, yellowish green color that appears blue when viewed obliquely. The color already appears during the condensation in a vacuum and is retained after cooling.

Examples for the production of effect pigments by the process according to the invention:

Example 1 The cholesteric liquid crystal polymer described in Example A is used

Polymer used. The cLCP granules are ground using an ultracentrifugal mill with a 0.1 mm sieve. The regrind is then sifted, the sifter setting being selected so that the average grain size is between 5 and 10 μm. A 35% non-aqueous dispersion in isobutanol is mixed with the viewed material.

The dispersion is applied to a Kapton film using a doctor blade, the gap width of which is 24 μm. After the dispersion application has dried, the powder is baked at 280 ° C. for 5 minutes. The film shows an orange color that appears green when viewed obliquely. The cLCP layer is very well developed and homogeneous. The layer thickness is 8 to 11 μm.

To produce the effect pigment, the carrier film is passed over a small-diameter deflection roller, the cholesteric polymer film peeling off. The polymer particles are ground in a universal mill. To reduce the particle size distribution, the millbase is sieved through a sieve with a mesh size of 63 μm. The effect pigment obtained is divided into a 2-

Component clear varnish incorporated, sprayed onto a black-primed sheet and coated with clear varnish. After baking, the varnish shows a copper color, which appears green when viewed at an angle.

Example 2

The cLCP dispersion job is prepared as described in Example 1. The polymer described in Example B is used as the cholesteric liquid crystal polymer.

After the dispersion application has dried, the polymer powder is covered with a second Kapton film and rolled over at 280 ° C. using a hand roller.

After cooling, the cover film is removed. The cLCP film shows a green color that appears blue when viewed obliquely. The layer thickness is 7

- 15 μm.

Effect pigment is prepared as described in Example 1. After baking in the varnish on a black background, the effect pigment shows a yellowish green color, which when viewed obliquely appears greenish blue. Example 3

The cLCP dispersion job is prepared as described in Example 1. The polymer described in Example A is used as the cholesteric liquid crystal polymer. After the dispersion application has dried, the polymer powder is covered with a silicon-coated aluminum foil and rolled over at 280 ° C. using a hand roller. After cooling, the aluminum cover film is removed and the cLCP film is post-annealed at 280 ° C. for 20 seconds. The film shows a brilliant orange color that appears green when viewed obliquely. The layer thickness is 8 to 17 μm.

Effect pigment is prepared as described in Example 1. After baking in the paint on a black background, the effect pigment shows a copper color that appears green when viewed at an angle.

Example 4

The cholesteric liquid crystal polymer described in Example A.

Polymer used.

The cLCP granules are ground using an ultracentrifugal mill with a 0.1 mm sieve. The regrind is then sifted, the sifter setting being selected so that the average grain size is between 5 and 10 μm.

With the sighted material, a 35% non-aqueous dispersion in

Mix isobutanol.

The dispersion is applied to a doctor blade with a gap width of 24 μm

Aluminum foil put on. After the dispersion application has dried, the powder is baked at 280 ° C. for 5 minutes. The film shows an orange

Color that appears green when viewed at an angle. The cLCP layer is very well developed and homogeneous. The layer thickness is 8 - 11 μm.

To produce the effect pigment, it is coated with cLCP

Put aluminum foil in semi-concentrated hydrochloric acid, whereby the aluminum carrier foil dissolves and the cholesteric polymer film remains. The

Polymer particles are ground in a universal mill. The regrind becomes Narrowing the particle size distribution through a sieve with a mesh size of 63 μm. The effect pigment obtained is worked into a two-component clear coat, sprayed onto a black-primed sheet and coated with clear coat. After baking, the varnish shows a copper color, which appears green when viewed at an angle.

Example 5

A 15% by weight dispersion of the cholesteric liquid crystal polymer

Example C (grain size D50 = 6-10 μm) in isobutanol is drawn onto an aluminum foil using a doctor blade whose gap width is 24 μm. After this

The coated aluminum foil is dried over a hot metal surface and the lower liquid crystal polymer layer is produced. The dwell time on the hot surface is 3 - 5 seconds at a surface temperature of 350 ° C. The film shows a green color, which appears blue when viewed obliquely. The cLCP layer is very well developed and homogeneous. The layer thickness is 3 - 5 μm. A 1% by weight dispersion of platelet-shaped graphite particles (for example Graphitan 7700®, commercially available from Ciba SC) in 2% aqueous carboxymethyl cellulose (Tylose H200X®, commercially available from Clariant) is applied to this layer using a 24 μm doctor blade and dried . Then the 15 wt .-% is again

Dispersion of the cholesteric liquid crystal polymer is applied with a 24 μm doctor blade and, after drying, again by pulling the film over a metal surface of 350 ° C. surface temperature with an average residence time of 3-5 seconds, the upper liquid crystal polymer layer is produced. The middle, light-absorbing graphite layer gives a covering

Polymer film that appears dark green when viewed vertically and dark blue when viewed obliquely. The total layer thickness is 7 - 12 μm. The effect pigment is prepared as described in Example 4. However, the aluminum foil is dissolved in semi-concentrated sodium hydroxide solution. The effect pigment shows a dark green color after baking in the varnish, which appears dark blue when viewed at an angle. Example 6

The polymer described in Example A is used as the cholesteric liquid crystal polymer.

The cLCP granules are ground using an ultracentrifugal mill with a 0.1 mm sieve. The regrind is then sifted, the sifter setting preferably being chosen so that the average grain size is between 5 and 10 μm.

A 35% non-aqueous dispersion in isobutanol is mixed with the viewed material. The dispersion is applied to a doctor blade with a gap width of 24 μm

Cellulose film pulled up. After the dispersion application has dried, the coated film is baked by a brief contact on a surface at 300 ° C. The film shows an orange color that appears green when viewed obliquely. The cLCP layer is very well developed and homogeneous. The layer thickness is 8 - 11 μm.

To produce the effect pigment, the coated film is drawn through an alkaline solution (5% sodium hydroxide solution) and the cholesteric polymer film is separated with a brush. The polymer particles are ground in a universal mill. The regrind is used to narrow the particle size distribution through a 63 μm sieve

Sieve mesh size. The effect pigment obtained is worked into a two-component clear coat, sprayed onto a black-primed sheet and coated with clear coat. After baking, the varnish shows a copper color, which appears green when viewed at an angle.

Claims

claims

1. A process for the production of thin films of thermoplastic cholesteric liquid-crystalline polymers, characterized in that one or more thermoplastic cholesteric liquid-crystalline polymers are applied as a non-aqueous dispersion to a planar substrate and are heated to or above the chiralization temperature.

2. The method according to claim 1, characterized in that the dispersion medium is an aliphatic hydrocarbon, an aromatic

Is hydrocarbon, an alcohol, an ester, a halogenated aliphatic or aromatic hydrocarbon, a ketone or a liquid polyhydroxy alcohol.

3. The method according to claim 1 or 2, characterized in that in the

Dispersion a dispersing additive and / or a thickener is included.

4. The method according to at least one of claims 1 to 3, characterized in that the thermoplastic cholesteric liquid crystalline

Polymer is a main chain polymer, a side group polymer, or a combination thereof.

5. The method according to claim 4, characterized in that the main chain polymer from a) 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) 0 to 50 mol% of one or more compounds from the group of aromatic dicarboxylic acids and cycloaliphatic dicarboxylic acids; c) 0 to 50 mol% of one or more compounds from the group of aromatic and cycloaliphatic diols and diamines; and d) 0.1 to 40 mol%, preferably 1 to 25 mol%, of chiral, bifunctional comonomers; the total amount being 100 mol% and the sum of a), b) and c) being 60 to 99.9 mol.

6. The method according to at least one of claims 1 to 5, characterized in that the polymer to be dispersed in the organic solvent is ground to a particle size (d ₅₀ ) of less than 30 microns, preferably less than 15 microns.

7. The method according to at least one of claims 1 to 6, characterized in that the planar substrate is a temperature-stable polymer film or tape, a metal foil or a metal tape, a glass plate or a tape, preferably a polyimide film, a cellulose film or an aluminum foil .

8. The method according to at least one of claims 1 to 7, characterized in that the non-aqueous dispersion applied to the planar substrate is dried, then covered with a temperature-stable film and rolled at the chiralization temperature.

9. The method according to at least one of claims 1 to 8, characterized in that the thermoplastic cholesteric liquid-crystalline polymers are mixed with dyes, or organic or inorganic pigments.

10. Process for the preparation of effect pigments with

Viewing angle dependent color, characterized in that a thin film of a thermoplastic cholesteric liquid-crystalline polymer is prepared according to one or more of claims 1 to 9, then separating the polymer film from the planar substrate and mechanically comminuting the polymer film into platelets whose diameter is at least twice as large is like the platelet thickness.