Process for coating and printing substrates

The invention relates to an inserting method for coating by means of spraying, rollcoating, dipping or with the aid of a casting nip or for printing substrates with a coating or a printing agent, characterized in that a polymerizable composition, the liquid-crystalline, polymerizable monomers, which two contain, contain, apply to the substrate and then carry out the polymerization, the coating agent or the printing medium<ul id="ul0001" list-style="none"><li>a₁) a chiral liquid crystalline monomer and<ul id="ul0002" list-style="none" compact="compact"><li>b) a polymeric binder and / or monomeric compounds which can be converted into the polymeric binder by polymerization or, in the case of dispersion coatings and printing inks, a dispersing aid d)</li></ul> contains, or the coating agent or the printing agent</li><li>a₂) an achiral liquid crystalline monomer,<ul id="ul0003" list-style="none" compact="compact"><li>b) a polymeric binder and / or monomeric compounds which can be converted into the polymeric binder by polymerization or, in the case of dispersion coatings and printing inks, a dispersing aid d) and</li><li>c) a non-liquid crystalline chiral compound</li></ul> contains.</li></ul>

The invention further relates to mixtures suitable as emulsion paints and printing pastes, which contain such polymerizable liquid-crystalline compounds, and to a process for the preparation of pigments from these compounds.

Surface-coated materials, whose color impression depends on the viewing angle, open up interesting application technology options.

GB 2 132 632 discloses liquid-crystalline (dihydro) cholesterol derivatives and mixtures of such derivatives which have a (meth) acrylate group and are polymerizable. According to this document, other substances which can be added to such derivatives and their mixtures are - as optional component (s) - crosslinkers which, however, themselves do not show any liquid-crystalline behavior. The main focus in the context of this document is on the production of liquid-crystalline films, which, however, should have only a low degree of crosslinking in accordance with the (dihydro) cholesterol derivatives used.

German patent application DE-A 35 35 547 describes a process in which a mixture of cholesterol-containing mono-acrylates can be processed into cholesteric layers via photo-crosslinking. As a linear polymer with the mesogenic molecular parts in the side chain, however, such a material is not mechanically very stable.

DE-A 42 40 743 describes pigments whose color depends on the viewing angle and which consist of oriented three-dimensionally crosslinked substances with a liquid-crystalline structure with a chiral phase and, if appropriate, further dyes and pigments. These pigments are suitable for dyeing paints, plastics, fiber raw materials, cosmetics or all kinds of printing inks, for example screen printing inks.

To produce these pigments, however, it is necessary to apply three-dimensionally crosslinkable liquid-crystalline substances with a chiral phase to a base, to crosslink them to a brittle layer on this base and to remove them from the base after crosslinking. The pigments obtained after grinding are then incorporated into coating systems or printing inks.

When used to coat substrates, these materials often prove disadvantageous because of the uneven surface.

Another disadvantage are the process temperatures which are clearly above room temperature and the multistage process with application to an intermediate substrate, comminution to pigments, preparation of semi-finished products, so-called pigment pastes and incorporation into the color mixture.

The object of the present invention was therefore to eliminate these disadvantages of the prior art.

Accordingly, the process described above for coating substrates was found.

The coatings according to the invention can be brittle or non-brittle after curing. In contrast to DE-A 42 40 743, non-brittle in the sense of the invention means that the cured coatings can no longer be removed from the base mechanically, for example by guiding the coated base over a deflection roller with a small diameter, without damaging it. Non-brittle coatings are particularly advantageous as paint-like coatings.

The color impression of the coatings according to the invention is based on the formation of cholesteric liquid-crystalline phases.

In a cholesteric phase, the liquid crystals form a helical superstructure that is perpendicular to the longitudinal axes of their molecules (H. Baessler, Solid State Problems XI, 1971).

The cholesteric phase has remarkable optical properties: a high optical rotation as well as a pronounced circular dichroism, which is created by selective reflection of circularly polarized light within the cholesteric layer. The colors, which appear different depending on the viewing angle, depend on the pitch of the helical overlays. structure, which in turn depends on the ability of the chiral component to twist. The pitch can be varied in particular by changing the concentration of a chiral dopant and thus the wavelength range of the selectively reflected light of a cholesteric layer.

Particularly stable coatings are obtained if the liquid-crystalline monomers a₁) and a₂) according to the invention contain two reactive groups which are accessible to polymerization. The chiral component c) preferably also contains at least one such reactive group, so that the diffusion of the compounds and a change in the color impression of the layers associated therewith is prevented.

Polymerization is understood to mean any type of build-up reaction of polymers, that is, addition polymerizations as chain reactions, addition polymerizations as step reactions and, although less preferred for paint coatings, condensation polymerizations.

A liquid-crystalline compound, but also a mixture of several of these liquid-crystalline compounds, can be used in the process according to the invention. In principle, all cholesteric liquid crystals are suitable. In addition, the cholesteric phase can be generated by doping a nematic liquid crystal system with chiral dopants. A mixture of several nematic liquid crystal components with a chiral dopant is preferably used.

According to the invention, the polymerizable liquid-crystalline compounds or mixtures thereof described in DE-A 44 08 170 and DE-A 44 08 171 are particularly suitable.

These compounds are polymerizable nematic liquid-crystalline materials which, alone or in mixtures with other polymerizable nematic liquid crystals, have broad nematic phase ranges and clearing temperatures below 140 ° C. and which can be processed below 140 ° C.

These compounds preferably correspond to the general formula I,         Z.¹- (Y¹-A¹)_v-Y²-MY³- (A²-Y⁴)_w-Z²     I. particularly preferably of the general formula Ia<chemistry id="chem0001" num="0001"><img file="EP0793693B2_D0001.tif" /></chemistry> where each ring can carry up to three identical or different substituents from the following group: C₁- to C₂₀-Alkyl, C₁- to C₂₀-Alkoxy, C₁- to C₂₀-Alkoxycarbonyl, C₁- to C₂₀-Mono-alkylaminocarbonyl, formyl, C₁- to C₂₀-Alkylcarbonyl, fluorine, chlorine, bromine, cyan, C₁- to C₂₀-Alkylcarbonyloxy, C₁- to C₂₀-Alkylcarbonylamino, hydroxy or nitro.

Of the radicals mentioned, chlorine, bromine, cyano, fluorine, hydroxy, methyl, ethyl, methoxy, ethoxy, methoxycarbonyl, formyl, acetyl and acetoxy and longer-chain radicals having at least 8 carbon atoms are preferred.

In formulas I and la, the radicals have the following meaning:<dl id="dl0001"><dt>Z.¹, Z²</dt><dd>reactive groups, via which a polymerization can be brought about, or residues containing such a reactive group,</dd><dt>Y¹, Y², Y³, Y⁴</dt><dd>a direct bond, -O-, -S-, -CO-O-, -O-CO-, -O-CO-O-, -NR¹-CO-O-, -O-CO-NO¹- or -NR¹-CO-NO¹-,</dd><dt>R¹</dt><dd>C.₁-C₄-Alkyl or hydrogen,</dd><dt>A¹, A²</dt><dd>Spacer and</dd><dt>V, W</dt><dd>0 or 1</dd><dt>M</dt><dd>a mesogenic group which preferably has the general structure of the formula II:         (TY⁵)_m-T II</dd></dl> in which the leftovers<dl id="dl0002"><dt>T</dt><dd>identical or different divalent isocycloaliphatic, heterocycloaliphatic, isoaromatic or heteroaromatic radicals,</dd><dt>Y⁵</dt><dd>same or different bridge members -CO-O-, -O-CO-, -CH₂O-, -OCH₂-, -CO-S-, -S-CO-, -CH₂-S-, -S-CH₂-, -CH = N- or -N = CH- or a direct bond and</dd><dt>m</dt><dd>1, 2, 3 or 4 mean.</dd></dl>

Preferred groups Z¹ and Z² are those that can be polymerized by a photochemical initiation step, including above all the vinyl group and the isopropenyl group and also the 4-vinylphenyl group and the I-chloroethenyl group.

Further preferred polymerizable groups Z¹ and Z² are those that contain an epoxy, cyanate or isocyanate residue.

Compounds with the cyanate residue are particularly preferred because they already react thermally to cyanurates. If they contain two cyanate groups, wide-mesh networks are obtained which are particularly advantageous for the formation of stable liquid-crystalline layers.

For polymerization, epoxides and isocyanates require further compounds with complementary reactive groups in the sense of polyaddition. For example, isocyanates can react with alcohols to form urethanes and with amines to form urea derivatives. The same applies to epoxies. The complementary reactive groups can a₁) or a₂) which is mixed with the former, or they can be introduced into the polymerization mixture by means of auxiliary compounds which contain 2 or more of these complementary groups.

For Y¹, Y², Y³ and Y⁴ In addition to a direct bond, ether and ester groups and the carbonate group (-O-CO-O-) are particularly preferred.

As spacer A¹ and A² can serve all groups known for this purpose. The spacers are usually via ester, ether or carbonate groups or a direct bond with Z¹ or Z² connected. Particularly suitable spacers are alkylene groups with 2 to 30, preferably 2 to 12, carbon atoms, which can be interrupted in the chain, for example, by oxygen in ether function or non-adjacent imino or methylimino groups. Fluorine, chlorine, bromine, cyan, methyl or ethyl are also suitable as substituents for the spacer chain. Representative spacers are for example - (CH₂)_p-, - (CH₂CH₂O)_q-CH₂CH₂-, - (CH₂CH₂S)_q-CH₂-CH₂-, - (CH₂CH₂NH)_q-CH₂CH₂-, <chemistry id="chem0002" num="0002"><img file="EP0793693B2_D0002.tif" /></chemistry> where q is 1 to 3 and p is 2 to 12.

The molecular parts with the outer aromatic rings of the mesogenic group<chemistry id="chem0003" num="0003"><img file="EP0793693B2_D0003.tif" /></chemistry> In the compounds of the formula Ia, independently of one another, preferably have one of the following structures:<chemistry id="chem0004" num="0004"><img file="EP0793693B2_D0004.tif" /></chemistry><chemistry id="chem0005" num="0005"><img file="EP0793693B2_D0005.tif" /></chemistry><chemistry id="chem0006" num="0006"><img file="EP0793693B2_D0006.tif" /></chemistry> where R² F, Cl, Br, C₁-C₂₀-Alkyl, C₁-C₂₀-Alkoxy, C₁-C₂₀-Alkylcarbonyl, C₁-C₂₀-Alkylcarbonyloxy, CHO or CN means and the substituents can also be mixed.

The part of the molecule with the middle aromatic ring<chemistry id="chem0007" num="0007"><img file="EP0793693B2_D0007.tif" /></chemistry> in formula la preferably has the following substitution pattern:<chemistry id="chem0008" num="0008"><img file="EP0793693B2_D0008.tif" /></chemistry><chemistry id="chem0009" num="0009"><img file="EP0793693B2_D0009.tif" /></chemistry><chemistry id="chem0010" num="0010"><img file="EP0793693B2_D0010.tif" /></chemistry><chemistry id="chem0011" num="0011"><img file="EP0793693B2_D0011.tif" /></chemistry><chemistry id="chem0012" num="0012"><img file="EP0793693B2_D0012.tif" /></chemistry><chemistry id="chem0013" num="0013"><img file="EP0793693B2_D0013.tif" /></chemistry><chemistry id="chem0014" num="0014"><img file="EP0793693B2_D0014.tif" /></chemistry> where r is 2 to 20, preferably 8 to 15.

Are particularly suitable as components a₂) for the coating or printing agent according to the invention compounds of the general formula I in which at least one of the pairs of residues Z¹ and Z², Y¹ and Y⁴, Y² and Y³, A¹ and A² consists of two different residues. Unsymmetrical compounds I or Ia of this type significantly expand the liquid-crystalline range of states of the coating compositions used according to the invention.

The compounds according to the invention are prepared by methods known per se. In general, the molecular parts Z¹, Z², A¹, A² and M linked by condensation reactions so that the bridge members Y¹ to Y⁴ be formed. The starting components are selected so that the corresponding esters or amides are formed. Acid chlorides with hydroxy or amino compounds are preferably reacted. This reaction principle also applies to the construction of the mesogenic group from the corresponding ring system components. The carbonate group is preferably formed by successive reaction of parts of the molecule carrying hydroxyl groups with phosgene. Further details on the preparation of the connections are given in German Offenlegungsschriften 44 05 316, 44 08 171 and 44 08 170.

The compounds of the formula I and Ia alone, in mixtures with one another or with other liquid-crystalline compounds have liquid-crystalline phase structures and can be converted into highly crosslinked polymers by radical or ionic polymerization processes while maintaining their liquid-crystalline order structure.

To set desired properties of the mixtures, it may be expedient to use more than two compounds of the formula I or Ia or else mixtures of compounds I or IA with other polymerizable liquid crystals.

The radicals T can optionally by C₁- to C₂₀-Alkyl, C₁- to C₂₀-Alkoxy, C₁- to C₂₀-Alkoxycarbonyl, C₁- to C₂₀-Monoalkylaminocarbonyl, formyl, C₁- to C₂₀-Alkylcarbonyl, fluorine, chlorine, bromine, cyan, C₁- to C₂₀-Alkylcarbonyloxy, C₁- to C₂₀-Alkylcarbonylamino, hydroxy or nitro may be substituted, with all alkyl-containing substituents short-chain having 1 to 6 carbon atoms and long-chain having 14 to 20 carbon atoms being preferred. Particularly preferred substituents are fluorine, chlorine, bromine, cyano, hydroxy or nitro. The residues T correspond to the following basic structures, for example:<chemistry id="chem0015" num="0015"><img file="EP0793693B2_D0015.tif" /></chemistry><chemistry id="chem0016" num="0016"><img file="EP0793693B2_D0016.tif" /></chemistry><chemistry id="chem0017" num="0017"><img file="EP0793693B2_D0017.tif" /></chemistry><chemistry id="chem0018" num="0018"><img file="EP0793693B2_D0018.tif" /></chemistry><chemistry id="chem0019" num="0019"><img file="EP0793693B2_D0019.tif" /></chemistry>

The following are particularly preferred as mesogenic groups M:<chemistry id="chem0020" num="0020"><img file="EP0793693B2_D0020.tif" /></chemistry><chemistry id="chem0021" num="0021"><img file="EP0793693B2_D0021.tif" /></chemistry><chemistry id="chem0022" num="0022"><img file="EP0793693B2_D0022.tif" /></chemistry><chemistry id="chem0023" num="0023"><img file="EP0793693B2_D0023.tif" /></chemistry><chemistry id="chem0024" num="0024"><img file="EP0793693B2_D0024.tif" /></chemistry><chemistry id="chem0025" num="0025"><img file="EP0793693B2_D0025.tif" /></chemistry><chemistry id="chem0026" num="0026"><img file="EP0793693B2_D0026.tif" /></chemistry><chemistry id="chem0027" num="0027"><img file="EP0793693B2_D0027.tif" /></chemistry><chemistry id="chem0028" num="0028"><img file="EP0793693B2_D0028.tif" /></chemistry><chemistry id="chem0029" num="0029"><img file="EP0793693B2_D0029.tif" /></chemistry><chemistry id="chem0030" num="0030"><img file="EP0793693B2_D0030.tif" /></chemistry><chemistry id="chem0031" num="0031"><img file="EP0793693B2_D0031.tif" /></chemistry><chemistry id="chem0032" num="0032"><img file="EP0793693B2_D0032.tif" /></chemistry><chemistry id="chem0033" num="0033"><img file="EP0793693B2_D0033.tif" /></chemistry><chemistry id="chem0034" num="0034"><img file="EP0793693B2_D0034.tif" /></chemistry><chemistry id="chem0035" num="0035"><img file="EP0793693B2_D0035.tif" /></chemistry><chemistry id="chem0036" num="0036"><img file="EP0793693B2_D0036.tif" /></chemistry><chemistry id="chem0037" num="0037"><img file="EP0793693B2_D0037.tif" /></chemistry>

Further suitable polymerizable, liquid-crystalline compounds are described, for example, in DE-C 36 04 757, EP-A 0 358 208 and in DJ Broer et al. in 14th Int. Liquid. Conf., Abstr. II, 921 (1992); H. Andersson, UW Gedde, A. Hult, Polymer, 1992, 33, 4014; RA, U. Hickmet, S. Lub, JA Higgins, Polymer, 1993, pages 34 ff., 1836 ff.

A characteristic feature of the coating or printing according to the invention is the appearance of cholesteric liquid-crystalline structures which cause the color impression. If the liquid-crystalline basic component is not itself chiral, the formation of a cholesteric phase can be caused by a chiral component c). In order to produce a stable cholesteric liquid-crystalline lacquer in which the cholesteric phase is fixed by crosslinking, this chiral component preferably contains reactive groups via which it can be connected to the other polymerizable coating agent components during the curing process. The chiral compounds c) preferably carry at least one polymerizable group, at least one spacer and at least one mesogenic group. Due to the similarity to the liquid crystalline component a₁) or a₂) such chiral compounds are particularly well suited as dopants for the production of cholesteric liquid crystal phases: such compounds have excellent solubility or miscibility behavior and usually high twisting power. Examples of such chiral components are described in German Offenlegungsschrift 43 42 280. The chiral compounds preferably correspond to the formula         (Z.¹-Y¹-A¹-Y²-MY³)_nX III, in which the residues Z¹, Y¹, Y², Y³, A¹ and M have the meaning given above:<dl id="dl0003" compact="compact"><dt>n</dt><dd>2nd to 6, preferably 2 or 3, and</dd><dt>x</dt><dd>means a chiral residue</dd></dl>

The residues A¹, M, Y¹, Y², Y³ and Z¹, since they are contained n times in III, may be the same or different.

Compounds III which are, as mesogenic groups M, residues of the formula IIa are particularly advantageous         (TY⁵)_s-T IIa included, where<dl id="dl0004"><dt>s</dt><dd>0 to 3, preferably 0 or 1 and</dd><dt>Y⁵</dt><dd>mean the bridge members defined above.</dd></dl>

Of the chiral radicals X of the compounds of the general formula III, those which derive from sugars, binaphthyl or biphenyl derivatives and optically active glycols, dialcohols or amino acids are preferred, inter alia because of the availability. In the case of sugars, pentoses and hexoses and derivatives derived therefrom should be mentioned in particular.

Examples of radicals X are the following structures, where the terminal lines each denote the free valences.

<chemistry id="chem0038" num="0038"><img file="EP0793693B2_D0038.tif" /></chemistry><chemistry id="chem0039" num="0039"><img file="EP0793693B2_D0039.tif" /></chemistry><chemistry id="chem0040" num="0040"><img file="EP0793693B2_D0040.tif" /></chemistry><chemistry id="chem0041" num="0041"><img file="EP0793693B2_D0041.tif" /></chemistry><chemistry id="chem0042" num="0042"><img file="EP0793693B2_D0042.tif" /></chemistry><chemistry id="chem0043" num="0043"><img file="EP0793693B2_D0043.tif" /></chemistry><chemistry id="chem0044" num="0044"><img file="EP0793693B2_D0044.tif" /></chemistry><chemistry id="chem0045" num="0045"><img file="EP0793693B2_D0045.tif" /></chemistry><chemistry id="chem0046" num="0046"><img file="EP0793693B2_D0046.tif" /></chemistry><chemistry id="chem0047" num="0047"><img file="EP0793693B2_D0047.tif" /></chemistry><chemistry id="chem0048" num="0048"><img file="EP0793693B2_D0048.tif" /></chemistry><chemistry id="chem0049" num="0049"><img file="EP0793693B2_D0049.tif" /></chemistry><chemistry id="chem0050" num="0050"><img file="EP0793693B2_D0050.tif" /></chemistry><chemistry id="chem0051" num="0051"><img file="EP0793693B2_D0051.tif" /></chemistry><chemistry id="chem0052" num="0052"><img file="EP0793693B2_D0052.tif" /></chemistry><chemistry id="chem0053" num="0053"><img file="EP0793693B2_D0053.tif" /></chemistry><chemistry id="chem0054" num="0054"><img file="EP0793693B2_D0054.tif" /></chemistry><chemistry id="chem0055" num="0055"><img file="EP0793693B2_D0055.tif" /></chemistry> in which<dl id="dl0005" compact="compact"><dt>L¹</dt><dd>C.₁- to C₄-Alkyl, C₁-C₄-Alkoxy, halogen, COOR², OCOR², CONHR² or NHCOR² is and R² a remainder of the definition of R¹ is.</dd></dl>

Are particularly preferred<chemistry id="chem0056" num="0056"><img file="EP0793693B2_D0056.tif" /></chemistry><chemistry id="chem0057" num="0057"><img file="EP0793693B2_D0057.tif" /></chemistry>

Chiral groups with the following structures are also suitable:<chemistry id="chem0058" num="0058"><img file="EP0793693B2_D0058.tif" /></chemistry><chemistry id="chem0059" num="0059"><img file="EP0793693B2_D0059.tif" /></chemistry>

Further examples are listed in German Offenlegungsschrift 43 42 280.

Liquid crystals with twisted cholesteric phases only show their special optical properties when large areas of the phase have a uniform orientation. The known methods for achieving this orientation are, for example, the interaction of the liquid crystal phase with orientation layers, the application of electrical or magnetic fields or the mechanical doctoring of the liquid crystal layers. These orientation methods require special technical devices that limit their use to simple substrates such as foils or other uniform surfaces.

A particular advantage of the method according to the invention is the possibility of applying the coating directly to the desired substrate and thus also to large surfaces of complex shape. This possibility is achieved according to the invention in that the liquid-crystalline compounds a₁) and a₂) and optionally the chiral compounds c) are mixed with a component b) which has a positive influence on the miscibility of the components with one another and in particular the viscosity and the flow behavior of the coating or printing agents. This component b) enables the spontaneous orientation of the liquid-crystalline phases at low temperatures without complicated technical orientation methods during the application process itself, that is to say when spraying, rollcoating, dipping, applying with the aid of a casting gap or the various printing processes.

Due to the different application techniques and also different requirements for the finished coating, other means are preferred for painting processes than for printing processes and for emulsion paints.

Component b) is particularly suitable for lacquer-like coatings as polymeric binders and / or monomeric compounds which can be converted into a polymeric binder by polymerization. Suitable such agents are, for example, polyesters, cellulose esters, polyurethanes, silicones, polyether- or polyester-modified silicones which are soluble in organic solvents. Cellulose esters such as cellulose acetobutyrate are particularly preferably used.

A reaction lacquer mixture particularly preferably contains those polymeric binders which contain reactive crosslinkable groups such as acrylic, methacrylic, α-chloroacrylic, vinyl, vinyl ether, epoxy, cyanate, isocyanate or isothiocyanate groups. Monomeric agents are also suitable as component b), especially the so-called reactive thinners known in paint production, such as, for example, hexanediol diacrylate or bisphenol A diacrylate. Even small amounts of such substances - usually already 0.1 to 1% by weight - bring about a considerable improvement in the flow viscosity and thus enable the application of thin, homogeneous lacquer layers in which the cholesteric liquid-crystal mixtures can orient themselves spontaneously. At the same time, these agents have a great influence on the mechanical properties of the hardened lacquer layer. By varying the concentration and selecting the binder, both the flow behavior and the elasticity of the paint can be easily adjusted in the flanged sense.

Mixtures suitable as reaction lacquers can contain a solvent or diluent as a further component. Examples of suitable solvents or diluents are esters, especially acetic acid esters, alcohols, lactones, aliphatic and aromatic hydrocarbons, amides, N-alkylpyrrolidones, especially N-methylpyrrolidone, as well as tetrahydrofuran and dioxane.

A particularly preferred reaction lacquer mixture is a solvent-free or low-solvent lacquer with water as a diluent.

The addition of adhesion aids to the paint according to the invention is advantageous for a stable surface coating. Suitable adhesion aids are, for example, silanes or compounds of the structure<chemistry id="chem0060" num="0060"><img file="EP0793693B2_D0060.tif" /></chemistry> where L² is a hydroxyl group, an isocyanate group or a crosslinkable radical, for example an acrylate or epoxy group, or where L² carries such a group.

Polymerization initiators can also be added to the paint, which decompose either thermally or photochemically and thus cause the paint to harden. Among the thermal polymerization initiators, preference is given to those which disintegrate between 20 and 180 ° C., particularly preferably between 50 and 80 ° C., and initiate the polymerization. In principle, all photoinitiators can be used for photochemical curing. In particular, mixtures of different initiators are used to improve curing. Examples of suitable photoinitiators are benzophenone and its derivatives, such as alkylbenzophenones, halogen-methylated benzophenones or 4,4'-bis (dimethylamizole-benzophenone) and benzoin and benzoin ethers, such as ethylbenzoin ether, benzil ketals such as benzil dimethyl ketal, acetophenone derivatives, such as hydroxy-2-methyl-1-phenylpropane -1-one and hydroxycyclohexylphenyl ketone are used. Acylphosphine oxides such as 2,4,6-trimethylbenzoyldiphenylphosphine oxide are very particularly suitable. Among the photochemically activatable polymerization initiators, preference is given to those which do not have a yellowing effect.

Particularly preferred polymerization initiators are boralkyl compounds and peroxides such as dibenzoyl peroxide and di-tert-butyl peroxide.

The photoinitiators, which, depending on the intended use of the coatings according to the invention, are used in amounts of between 0.01 and 15% by weight, based on the polymerizable components, can be used as individual substances or, because of advantageous synergistic effects, also in combination with one another .

Initiators which have charged structures are preferably used for cationic polymerizations. In particular, substances are used, some of which are used in combination with acylphosphine oxides, for example:<chemistry id="chem0061" num="0061"><img file="EP0793693B2_D0061.tif" /></chemistry> and derivatives of these compounds.

If desired, stabilizers against UV and weather influences can also be added to the paints. Derivatives of 2,4-dihydroxybenzophenone, derivatives of 2-cyano-3,3-diphenylacrylate, derivatives of 2,2 ', 4,4'-tetrahydroxybenzophenone, derivatives of orthohydroxyphenylbenzotriazole, salicylic acid esters, orthohydroxyphenyl-S-triazines or sterically hindered amines. These substances can be used alone or preferably in the form of mixtures.

Pigments, dyes and fillers can also be added to the coating systems.

Inorganic pigments include iron oxides, titanium dioxide and the various types of carbon black.

Organic pigments are, for example, those from the class of monoazo pigments (e.g. Products derived from acetoacetic acid derivatives or from β-naphthol derivatives), monoazo dyes and their metal salts, such as β-oxynaphthoic acid dyes, disazo pigments, condensed disazo pigments, isoindoline derivatives, derivatives of naphthalene or perylene tetraonoquinone, dinoquinone dehydroquinone, dinoquinone dino carbonic acid, anthraquinone, dinoquinone dino carbonic acid, anthraquinone, dinoquinone dinoquinone, dinoquinone dino carbonic acid, anthraquinone dinoquinone, dinoquinone dioquinone, dinoquinone dino carboxylic acid Phthalocyanine pigments or basic dyes such as triarylmethane dyes and their salts.

Effect pigments such as aluminum particles, mica or coated mica, micas or the commercially available platelet-shaped effect pigments with different chemical structures can be considered as further pigments.

Examples of suitable fillers are rutile, anatase, chalk, talc and barium sulfate.

Suitable as additional dyes are all which dissolve in the coating composition at least in a concentration of 0.1 mol%. Dichroic dyes are particularly suitable. The proportion of pigments, dyes or fillers is generally up to 40% by weight, preferably up to 10% by weight, based on the mass of the liquid-crystalline compounds.

The varnishes have numerous advantages. Thus, the substrates coated according to the invention have a high surface quality and an improved color impression compared to systems which were produced from polymeric or oligomeric cholesteric liquid crystal pigments.

For example, a vehicle painted according to the invention appears to the viewer in different colors from different angles, the high surface quality affording the body a high level of protection against corrosion or mechanical damage and a high gloss. This can be improved by applying a clear coat.

Due to the helix structure of the polymer-fixed cholesteric liquid-crystalline phase, part of the light hitting the surface is reflected with different wavelengths depending on the direction. The intensity of this color impression can be intensified by applying at least two lacquer layers according to the invention with the same selective reflection wavelength, but with opposite helix mobility, one above the other. For example achieved in that the lacquer layers each contain compounds as a chiral component, the helical direction of rotation of which is opposite and of a similar size.

Further interesting color effects can be achieved by layering several layers of lacquer on top of each other, the layers differing in their selective reflection wavelength.

In this way, an even greater number of color shades depending on the viewing angle can be generated.

Also preferred are coating processes in which the application and subsequent curing take place at temperatures of 10 to 130 ° C., particularly preferably at 20 to 80 ° C.

In a further preferred embodiment of the method according to the invention, the surface coating is carried out by means of a printing method.

All common printing methods (e.g. high, low, flexo, offset, screen printing) can be used. Here, too, there is a spontaneous orientation of the liquid crystals through the application process itself.

Printing processes within the meaning of the invention are also those in which the coating agent is applied to a substrate such as paper or plastic, for example by using a ballpoint pen or fountain pen.

Since the reflection range can be adjusted from infrared to ultraviolet light, the printing inks according to the invention can also be used to produce markings and security marks which are invisible to the human eye. They can be detected on the basis of circular polarization or angle dependency.

Since other requirements are placed on the mechanical properties of the coating and on the flow behavior required for processing in printing processes, other compositions are preferred for these processes. As components a₁), a₂) and c) the same compounds come into consideration as are used for painting processes. In contrast to component b), however, dispersion aids are preferably used as component d). These dispersing agents impart a particularly good miscibility of all components of the printing paste and a particularly uniform application to the substrate. At the same time, the dispersing agent serves to adjust the desired flow viscosity, so that a spontaneous orientation of the cholesteric liquid crystals occurs, as with the coatings. The use of a dispersing agent usually means that the solvents commonly used in printing processes, such as cyclohexane, tetrahydrofuran, toluene, xylene, styrene or acrylic esters, can be completely dispensed with.

In addition to the viscosity, the high surface tension of the cholesteric liquid crystal systems also affects the pressure behavior. It easily leads to structure formation and wetting problems in printing, which manifests itself in uneven, rough printing layers.

This hindering property can also be positively influenced by admixing dispersing aids, so-called hyperdispersants, without the optical properties of the cholesteric liquid crystal phases suffering. Hyperdispersants of the alkenyl or alkyl succinic acid derivative type in particular are well suited for these purposes and, in addition to being easier to process, even increase the colored interference effect.

Particularly suitable dispersing agents are compounds of the general formulas IVa to IVc<chemistry id="chem0062" num="0062"><img file="EP0793693B2_D0062.tif" /></chemistry><chemistry id="chem0063" num="0063"><img file="EP0793693B2_D0063.tif" /></chemistry><chemistry id="chem0064" num="0064"><img file="EP0793693B2_D0064.tif" /></chemistry> in which the variables have the following meaning:<dl id="dl0006"><dt>X₁, X₂</dt><dd>Oxygen, NH, NO⁵ or NO⁶,</dd><dt>R³, R⁴</dt><dd>Hydrogen or an aliphatic radical with a molecular weight of up to 5000, one of the radicals R³ or R⁴ Hydrogen means</dd><dt>R⁵, R⁶</dt><dd>Hydrogen or an aliphatic or aromatic radical with a molecular weight of up to 50,000,</dd></dl> where if X₁ and / or X₂ Oxygen Oxygen means R⁵ and / or R⁶ can also be a monovalent cation or the equivalent of a divalent cation.

In general, commercially available compounds or mixtures thereof are used as dispersing agents IVa to IVc. These compounds are obtained by reacting fumaric or maleic acid derivatives with olefins. R radicals are preferred³ or R⁴, which are derived from the following olefins:

Olefins with 8 to 40 carbon atoms, which preferably have a terminal double bond, oligo or polyolefins, which are derived from monoolefins with 2 to 30 carbon atoms and can be substituted, for example, with chlorine and have an average molecular weight of 100 to 5000, preferably 500 to 2000 . Particularly preferred radicals R¹ and R⁴ are derived from diisobutene, dibutadiene, polyisobutylene with 3 to 90 isobutylene units, polypropylene with 3 to 120 propylene units, polyethylene with 4 to 180 ethylene units and polybutadiene with 3 to 90 butadiene units, a polyisobutylene with 3 to 40 isobutylene units being particularly noteworthy.

The compounds IVa to IVc are generally used as production-related mixtures. Compounds which contain more than one succinic acid derivative can also be produced, for example when using polyunsaturated olefins. These compounds are also effective components of the dispersing agent mixtures.

The molecular parts X₁R⁵, X₂R⁶ and NO⁵ are introduced into the compounds IVa and IVb by reacting reactive succinic acid, maleic acid or fumaric acid derivatives, such as anhydrides or acid chlorides. The reaction takes place with the corresponding alcohols or primary or secondary amines.

Possible amines for this implementation are: aliphatic, cycloaliphatic and aromatic, primary and secondary mono- and polyamines, heterocyclic mono- and polyamines, alkylene polyamines and polyalkylene polyamines, branched polyalkylene amines, ether amines, polyether amines, Oxyalkylendiamine, polyoxyalkylenediamines, polyoxyalkylenepolyamines, hydroxyalkyl, and polyalkylene glycol-substituted amines, aminosulfonic, aminocarboxylic acids, aminophosphonic acids, Aminophosphonsäureester as well as amines, which contain tertiary or quaternary amino functions.

Preferred amine components are N, N-dimethyl-1,3-diaminopropane, N, N-dimethyl-dipropylene tetramine, diethylene tetramine, triethylene tetramine or bis- (β-aminopropyl) -1,2-diaminoethane.

Suitable alcohols for the reaction are: monohydric and polyhydric alcohols, dialcohols, trial alcohols, ether alcohols, polyalkylene glycol ethers, alkyleneoxy adducts with alcohols and phenols, hydroxyalkyl heterocycles, hydroxyalkyl aromatics, hydroxycarboxylic acids, hydroxysulfonic acids, hydroxyphosphonic acids, polyalcohols or alcohols containing tertiary unions or tertiary amines.

Particularly suitable salts of the succinic acid derivatives are the ammonium salts, including preferably the quaternary ammonium salts, and sodium, potassium and calcium salts.

Since polymerizable printing inks are generally adhered photochemically, a photoinitiator is preferably added to the cholesteric liquid-crystalline mixture in addition to the compounds described. All commercially available products are suitable as photoinitiators, for example the compounds described for the paint mixtures.

To mix the liquid-crystalline printing paste with the dispersing aid additive and then printing, the procedure is generally such that the additive and then the photoinitiator are added to the pasty liquid-crystal material. The photoinitiator is expediently added in the form of an approximately 2.0% solution of the photoinitiator in an organic solvent which is expediently stirred in with gentle heating of the liquid crystal material. However, the additive or, if desired, an additive combination and the photoinitiator can also be stirred in at the same time. If the photoinitiator is sensitive to UV light, work under yellow light. In offset printing machines with variable ink application, the highest possible film thickness of the print is set. During and immediately after the printing process, oxygen-sensitive liquid crystal compounds are flushed with an inert gas and, after a dwell time, which can be between 0.01 and 10 minutes depending on the substance, crosslinked by exposure to light. Depending on the intensity of the irradiation, curing with light of the appropriate wavelength can take between a few seconds and several minutes. The liquid crystalline film is then dry and shows the desired optical behavior.

The angle-dependent color changes are particularly impressive when the liquid-crystalline film is applied to a black background, ie to a non-selectively absorbing substrate. Interesting variants can also be achieved with selectively absorbing substrates or by adding carbon black or color pigments to the liquid crystal material.

The area of ​​application for liquid crystal prints is particularly in the decorative area and in the area of ​​marking banknotes and similar papers which are to be protected against counterfeiting. It includes prints of all kinds, whereby the printing of substrates such as paper, cardboard, leather, foils, cellular glass, textiles, plastics, glass, ceramics and metals is possible. Various printing techniques can be used, e.g. Screen printing, flexo printing, offset printing, ink jet printing, gravure printing, letterpress printing, pad printing, heat seal printing and other transfer printing methods. Application using a casting gap is also possible, as a result of which very thin, uniform layers can be obtained. Anilox rollers with a doctor blade (modified coating unit) or conventional coating units can also be used for printing. The substrates can be colored black, colored or white or pigmented and can have profiles or pre-printed patterns of any kind. The liquid crystal coating always gives the printed object a color angle that is particularly interesting in terms of viewing angle, ie a color that changes with the viewing angle, the intensity of which depends on the optical absorption capacity of the substrate.

An interesting embodiment of the method according to the invention consists in the production of pigments by offset printing. This printing technique makes it possible to apply and harden a cholesteric liquid-crystalline printing paste as identically dimensioned dots on a substrate, for example a film or sheet. The resulting pigment particles are almost identical in shape and size, which can be adjusted very precisely by varying the printing parameters. When the substrate is suitably pretreated with an adhesion-reducing agent, the pigments can then be easily removed from the substrate and used as usual as color pigments. Due to their narrow size distribution, these pigments can be incorporated very well into paint systems and, in contrast to the pigments described in DE-A 42 40 743, provide paint surfaces without roughness and of high surface quality.

The mixtures according to the invention can be applied to the substrates particularly advantageously in the form of aqueous dispersions. In addition to the liquid-crystalline and chiral compounds, such dispersions contain the customary binders and, if desired, further auxiliaries, for example light stabilizers and preservatives, pigments and soluble dyes. The liquid crystal content of these dispersions, which are suitable as paints for interior and exterior coatings, is generally between 20 and 95% by weight.

The addition of dispersants is of particular importance. These agents influence the properties of the dispersions in such a way that after the evaporation of the diluent, that is to say as a rule the water, the liquid crystals spontaneously orientate themselves with the color effects associated therewith.

Water-soluble, high molecular weight organic compounds with polar groups, such as polyvinylpyrrolidone, copolymers of vinyl propionate or acetate and vinylpyrrolidone, partially saponified copolymers of an acrylic ester and acrylonitrile, polyvinyl alcohols with different residual acetate content, cellulose ethers, gelatin or mixtures of these substances are preferably used as dispersing agents. Particularly preferred protective colloids are polyvinyl alcohol with a residual acetate content of less than 35, in particular 5 to 30 mol percent and / or a vinylpyrrolidone / vinyl propionate copolymer with a vinyl ester content of less than 35, in particular 5 to 30 percent by weight.

Both nonionic and, in special cases, ionic emulsifiers can be used. Preferred emulsifiers are longer-chain alcohols or phenols of different degrees of ethoxy and / or propoxylation (adducts of 4 to 50 mol of ethylene oxide and / or propylene oxide). Combinations of the above-mentioned protective colloids with such emulsifiers are particularly advantageous since they give very finely divided dispersions.

Other suitable dispersants are, for example, dihexylsulfosuccinate, sulfosuccinate half-esters, the sodium salts of dodecylbenzenesulfonic acid and pentadecanesulfonic acid, potassium oleate, sodium lauryl sulfate, alkyl polyglycosides, isooctylphenol, isononylphenol, C.₁₂-C₁₈Fatty alcohols and fatty alcohol alkoxylates,

Dispersing aids based on polysiloxane are also particularly suitable.

The dispersing agents described are suitable for the preparation of oil-in-water emulsions. However, it is also possible to prepare dispersion coating compositions based on water-in-oil emulsions. Emulsifiers and emulsifier mixtures such as are described, for example, in EP-A 0 623 630 are particularly suitable for such dispersions. Suitable dispersing agents are also sorbitan monostearate, sorbitan monopalmitate, sorbitan tristearate, sorbitan monooleate, sorbitan sesquioleate, polyoxyethylene sorbitol ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether and polyoxyethylene oleyl ether.

Mini emulsions are also suitable as the basis for the coating compositions according to the invention. Mini emulsions have the advantage of forming particularly stable emulsions and are therefore particularly stable in storage. To produce the mini-emulsions, for example, the emulsions described above, which typically have droplet diameters in the micrometer range, are homogenized using a high-pressure homogenizer. In this way, emulsions with droplet diameters&gt; 200 nm are obtained in which no phase separation can be observed for weeks.

To produce the liquid crystal dispersions, the liquid crystalline mixture consisting of components a₁) and / or a₂) and c) if desired mixed with a small amount of a solvent such as tetrahydrofuran, dioxane, acetone, methyl ethyl ketone, the propanols, the butanols, ethyl acetate, butyl acetate, methylene chloride, the xylenes or toluene or else water in order to reduce the viscosity. The addition of a polymeric binder such as cellulose acetate butyrate is also suitable for this purpose. However, the dispersing aid, which can also be added as an aqueous solution, is preferably added directly to the liquid-crystalline mixture. The mixture is homogenized intensively, for example by stirring. Then water is added and again homogenized thoroughly. The amount of water depends on the desired use. 20 to 80% by weight, particularly preferably 40 to 60% by weight, of water are preferably added, based on the total amount of the finished dispersion. For processing, the dispersions can be diluted with water, to which a dispersing aid can also be added, to the desired viscosity and colorant concentration.

For curing the films formed from the dispersion, thermal processes or radiation processes such as light or electron beam curing are possible, as for the coating mixtures, depending on the type of polymerizable group. The addition of polymerization initiators, as described for the coating mixtures, is also advantageous for the curable dispersion films.

The advantage of dispersion coatings is that they are easy to process. The dispersions have low viscosities, can be prepared without solvents and therefore do not require any ventilation devices and can be applied by all known, simple application techniques such as brushing, rolling, spraying, printing, dipping or through a casting gap. The coating process according to the invention also gives rise to spontaneous orientation from the dispersion, so that the desired color impression, which is dependent on the viewing angle, is produced.

Examples

example 1

Production of a liquid crystal mixture of structure la

<maths id="math0001" num=""><img file="EP0793693B2_D0065.tif" /></maths> a, b = 2, 4 or 6

A mixture of 100 ml of pyridine and 14.4 g (100 mmol) of 2-chlorohydroquinone was gradually dissolved out at 20 ° C<ul id="ul0004" list-style="none" compact="compact"><li>18.78 g (67 mmol) 4- (2-acryloxyethoxylbenzoic acid chloride,</li><li>19.92 g (67 mmol) of 4- (2-acryloxybutoxy) benzoic acid chloride and</li><li>20.65 g (67 mmol) of 4- (2-acryloxyhexoxy) benzoic acid chloride</li></ul> added in 100 ml of toluene. The reaction mixture was then kept at 60 ° C. for a further 4 h, after which it was added to a mixture of ice and hydrochloric acid and worked up as usual.

Due to the different alkylene spacers in the starting compounds, a statistical mixture of 9 possible isomers was obtained (yield 89%), which shows a more advantageous phase behavior than a single compound. Phase behavior: N 91 - 98 ° C l

Example 2

Preparation of a cholesteric liquid crystal mixture A

9.5 g of the liquid crystal mixture prepared in Example 1, 0.5 g of 1,4: 3,6-dianhydrosorbitol-2,5-bis (4 '- (6-acryloxyhexoxy) benzoic acid) ester and 20 ml of dichloromethane were mixed. The solvent was then removed in vacuo at 70 ° C.

Example 3

Preparation of a cholesteric liquid crystal mixture B

9.3 g of the liquid crystal mixture prepared in Example 1, 0.7 g of 1,4: 3,6-dianhydrosorbitol-2,5-bis (4 '- (6-acryloxyhexoxy) benzoic acid) ester and 20 ml of dichloromethane were mixed. The solvent was then removed in vacuo at 70 ° C.

Example 4

Preparation of a cholesteric liquid crystal mixture C

10.0 g of the liquid crystal mixture prepared in Example 1, 0.5 g of 1,4: 3,6-dianhydrosorbitol-2,5-bis (4 '- (6-acryloxyhexoxy) benzoic acid) ester and 20 ml of dichloromethane were mixed. The solvent was then removed in vacuo at 70 ° C.

Example 5

Preparation of a cholesteric liquid crystal mixture D

The liquid crystal mixture was prepared analogously to Example 3, but the chiral component used was 1,4: 3,6-dianhydrosorbitol-2,5-bis (4'- (2-acryloxyethoxybenzoic acid ester).

Example 6

Production of a cholesteric sprayable lacquer

10.5 g of the cholesteric liquid crystal mixture C were stirred with 0.15 g of 2,4,6-trimethylbenzoyldiphenylphosphine oxide, 1 g of toluene and 4 g of ethyl acetate until a homogeneous solution was obtained. This cholesteric mixture was filled into a high-pressure spray gun (Proxxon, Gala 500) and sprayed at 3 bar pressure onto a black painted metal, glass or paper surface. The fine drops were cleaned with a mercury discharge lamp (80 W / cm²) Irradiated for 5 seconds until the surface was tack-free. The spraying process was repeated until a uniform surface, uniformly covered by cholesteric liquid crystal, was obtained. The diameter of the platelet-shaped bodies resulting from the spraying on the treated surface was 20 to 50 μm.

Example 7

The procedure was as in Example 6, using 0.15 g of a thermochemical initiator. The paint was sprayed onto a black painted metal surface and then crosslinked by thermal treatment (120 min at 65 ° C).

Example 8

Production of a cholesteric ink

5 g of the cholesteric liquid crystal mixture D were stirred under yellow light with 0.075 g of 2,4,6-trimethylbenzoyldiphenylphosphine oxide, 0.25 g of toluene and 1.5 g of graphite pigment until the pigment and the starter were uniformly distributed. The mixture thus produced could be filled into a print cartridge and written on black paper using a fountain pen. After the photopolymerization, a typeface with a color change from bronze red to green was obtained. This mixture could also be used as a coating color for brushing larger areas with a brush or similar application agent. The mixture could also be applied using the screen printing process.

Example 9

Cholesteric liquid crystalline paint

1.4 g of toluene, 0.5 g of polyvinyl alcohol and 1 ml of ethanol were added to 2 g of cholesteric liquid-crystalline mixture A and the mixture was dispersed. A cloudy, low-viscosity mixture was formed. This was applied to the black-painted substrate using a spray gun as in Example 6. After the solvent had been evaporated off, the liquid-crystalline layer formed which reflected in the red was cured by irradiation with light. The cured layer was stable against the influence of solvents, temperature and light.

Example 10

Black pigmented cholesteric liquid crystalline paint

0.3 g of black pigment was added to the mixture given in Example 9 and homogenized. This mixture was applied to an uncoated metallic substrate by spraying as in Example 6. After ventilation, a well covering, red reflective layer was created, which was cured by irradiation with light. The cured layer was stable against the influence of solvents, temperature and light.

Example 11

0.3 g of black pigment and 0.04 g of a UV stabilizer were added to the mixture given in Example 9 and homogenized. This mixture was applied to an uncoated substrate by spraying. After ventilation, a well covering, red reflective layer was created, which was cured by irradiation with light. The cured layer was stable against the influence of solvents, temperature and light.

Example 12

Cholesteric liquid crystalline paint

To 10 g of the cholesteric liquid-crystalline mixture B, 0.4 g of a 20% solution of CAB (cellulose acetate butyrate) in butyl acetate and 7 g of butyl acetate were added and the solution was homogenized. A slightly viscous, transparent solution resulted. This mixture was sprayed several times and in the meantime vented onto a black primed surface. After the last order had flashed off, the polymerisation was carried out photochemically. For this purpose, the coated surface was exposed to a UV lamp (OSRAM-Nitraphot, distance 30 cm, nitrogen atmosphere) for 30 seconds. The result was a uniform, well-running, firmly adhering film with a layer thickness of 16 μm, which had a color impression dependent on the viewing angle with a color change from green to blue.

Example 13

Cholesteric liquid crystalline paint

0.04 g of a 20% solution of CAB (cellulose acetate butyrate) dissolved in butyl acetate and 1.4 g of butyl acetate were added to the cholesteric liquid-crystalline mixture A and the solution was homogenized. A slightly viscous, transparent solution was created. This mixture was applied to a black-primed surface by repeated spraying and flashing off in the meantime. After the last order had flashed off, the polymerisation was carried out photochemically. The result was a uniform, well-running, firmly adhering film with a layer thickness of 15 μm, which had a color impression dependent on the viewing angle with a color change from red to green.

Example 14

According to Example 13, a cholesteric liquid-crystalline lacquer was produced. After curing, a commercially available clear coat was applied and then cured. The coating produced in this way had an increased gloss and an improved resistance to light and moisture compared to a coating without a clear lacquer.

Such a paint build-up consisting of ETL, filler, cholesteric paint and clear coat was subjected to a short weathering test (WOM). There was no color difference and no delamination between the layers.

Example 15

0.3 g of a black pigment was added to 2 g of the sprayable, brushable and dipped paint from Example 12 and the resulting dispersion was homogenized. A black, low-viscosity dispersion resulted. This was applied to a white primed surface by repeated spraying and flashing off in the meantime.

After the last order had been flashed off, polymerization was carried out photochemically using a mercury discharge lamp (80 W / cm). The result was a uniform, well-running, firmly adhering film with high opacity, which had an angle-dependent color impression (green / blue).

Example 16

The auxiliary BYK 055 (manufacturer: Byk, Wesel) was added to 2 g of the paint from Example 13 in an amount of 0.01 g of the delivery form. A slightly viscous, transparent solution was created. This mixture was applied to a black-primed surface by repeated spraying and flashing off in the meantime. After the last order had flashed off, the polymerisation was carried out photochemically. The result was a uniform, well-running, firmly adhering film with a high surface hardness, which had an angle-dependent color impression with a color change from red to green. The layer thickness was 14 µm.

Example 17

The auxiliary BYK 057 (manufactured by Byk, Wesel) was added to 2 g of the paint from Example 13 in an amount of 0.01 g of the delivery form. A slightly viscous, transparent solution was created. This mixture was applied to a black-primed surface by repeated spraying and flashing off in the meantime. After the last order had flashed off, the polymerisation was carried out photochemically. The result was a uniform, well-running, firmly adhering film with a high surface hardness, which had an angle-dependent color impression with a color change from red to green. The layer thickness was 14 µm.

Example 18

Comparison test: printing paste without dispersing agent

The pasty cholesteric liquid crystal mixture A was heated to 40 ° C. on a water bath under nitrogen. 1.5% by weight (based on the liquid crystal material: 2,4,6-trimethylbenzoyldiphenylphosphine oxide) were added with stirring and the mixture was stirred in homogeneously for 10 minutes. After cooling to 25 ° C., a FOGRA printing machine with variable ink application was applied to a white cardboard printing medium printed with black fields with 1.5 g / m color application in offset. It was worked under yellowish.

After a dwell time of 5 minutes under nitrogen, the printing film was cured for 3 minutes by light irradiation with a UV lamp (200 to 230 V / 300 W 4FZ).

The result was a coating that was visible over a black background and changed slightly between green and copper-colored, which had a granular structure and was also mechanically rough. The light microscopic image showed that the coating was not coherent, but consisted of many small liquid crystal islands on an untreated black background.

Example 19

The liquid crystal paste was heated to 40 ° C. on a water bath under nitrogen as in Example 18. With stirring, 0.5% by weight of the PIBSA additive (polyisobutylene succinic anhydride) (based on the weight of the liquid crystal material) was stirred in for 2 minutes, then 1.5% by weight (based on the wiping of the liquid crystal material) became 24.6 -Trimethylbenzoyldiphenyiphosphinoxid added and stirred for 10 minutes. Under yellow light was on a FOGRA printing machine with variable ink application on white cardboard with black fields with 1.5 g / m² Color application printed in offset. Rub time: 40 sec.

After a dwell time of 3 minutes under nitrogen, the printing film was cured by exposure to light with a UV lamp as in Experiment 1.

The result was a clearly visible film which alternated between green and copper-colored on a black background, which appeared to be significantly more vivid and homogeneous than the one produced in Example 18. The light micrograph showed that the coating was significantly more coherent than in Example 18 and that, compared to Example 18, fewer areas of the substrate were not wetted or coated. The mechanical roughness of the film decreased.

Example 20

The procedure was as in Example 19, with the only difference that 5% by weight of PIBSA additive, based on the weight of the liquid crystal, was added to the liquid crystal material.

The result was a film whose optical properties and homogeneity were further improved. The film appeared more vivid than in Example 19 and was more homogeneous.

Example 21

The procedure was as in Example 19, with the difference that 10% by weight of PIBSA additive, based on the weight of the liquid crystal, were added to the liquid crystal material.

A film was created, the homogeneity of which was further improved. As far as the optical properties of the film were concerned, they were of slightly lower quality than in Example 20. The film appeared somewhat darker and the color change from green to copper was impaired.

Example 22

The procedure was as in Example 20, with the difference that instead of the flat printing (Examples 18 to 21), discrete dots were printed with a screened printing roller (56 screen).

A screen with graduated intensity could be printed on paper as well as on transparent plastic film.

Microscopic examinations showed that the halftone dots had a thickness of 1.5 µ and a diameter of 5 µ. The print images showed a color change comparable to full-surface printing.

Example 23

The procedure was as in Example 19, with the difference that 5% by weight of PIBSA additive, 1% by weight of carbon black and 1.5% by weight of 2,4,6-trimethylbenzoyldiphenylphosphine oxide were simultaneously added to the liquid crystal material. After stirring for 10 minutes, printing was carried out under yellow light on the FOGRA machine.

An extremely brilliant film, which alternated between green and copper-colored, over black background was obtained, which was homogeneous and in optical quality even exceeded the print from example 20.

Example 24

At room temperature (25 ° C.), 5% by weight of the PIBSA additive was stirred into the liquid crystal paste under nitrogen. After stirring for five minutes, 1.5% by weight of 2,4,6-trimethylbenzoyldiphenylphosphine oxide was added and the mixture was stirred for a further 10 minutes. The paste was then applied using a screen-printing machine with an automatic doctor blade (mesh size of the screen: 70 openings per inch²) printed on white cardboard with a black pattern.

After curing the film under a UV lamp (200 to 230 V / 300 W 4FZ) for 5 minutes, a decorative colored coating with a viewing angle-dependent color tone was obtained, which, particularly over black, clearly changed between copper-colored and green.

Example 25

Aqueous emulsion paint with a color impression depending on the viewing angle.

4.5 g of cholesteric liquid crystal mixture A, 0.2 g of 2,4,6-trimethylbenzoyldiphenylphosphine oxide, 0.08 g of cellulose acetobutyrate and 1.5 g of 33% by weight aqueous polyvinylpyrrolidone solution were homogenized by intensive stirring for 30 minutes. 4 g of water were then added to this dispersion and the mixture was homogenized for a further 20 min by further stirring. There was an aqueous dispersion of a cholesteric liquid crystal in water.

Example 26

The dispersion obtained in Example 25 was applied by brushing onto a black lacquered sheet. After flashing, a color layer appeared blue when viewed vertically, which changed color to violet when the direction of view deviated from the vertical. The layer thus obtained was then hardened by exposure to UV light. The color impression was retained.

Example 27

The dispersion obtained in Example 25 was applied by spraying to a black lacquered sheet. After flashing, a color layer appeared blue when viewed vertically, which changed color to violet when the direction of view deviated from the vertical. The layer thus obtained was then hardened by exposure to UV light. The color impression was retained.

Example 28

Low-solvent, water-thinnable emulsion paint.

3rd g of cholesteric liquid crystal mixture B, 0.2 g of 2,4,6-trimethylbenzoyldiphenylphosphine oxide and 0.08 g of cellulose acetobutyrate were dissolved in 1.5 g of butyl acetate. 1.5 g of 33% by weight aqueous polyvinylpyrrolidone solution were added to this solution and homogenized by intensive stirring for 30 minutes. 4 g of water were then added to this dispersion and briefly homogenized.

The result was a strongly light-scattering, low-solvent, aqueous dispersion.

Example 29

The dispersion obtained in Example 28 was applied by brushing onto a black painted sheet. After flashing, a color layer appeared green when viewed vertically, which changed color to blue when the direction of view deviated from the vertical. The layer thus obtained was then hardened by exposure to UV light. The color impression was retained.

Example 30

The dispersion obtained in Example 28 was applied by spraying to a black lacquered sheet. After flashing off, a color layer appeared green when viewed vertically, which changed color to blue when the viewing direction deviated from the vertical. The layer thus obtained was then hardened by exposure to UV light. The color impression was retained.

Example 31

The dispersion obtained in Example 28 was applied by brushing onto a wooden substrate. After flashing off, a color layer appeared green when viewed vertically, which changed color to blue when the viewing direction deviated from the vertical. The layer thus obtained was then cured by exposure to UV light to obtain the color impression.

Example 32

Dispersion coating agent based on water-in-oil emulsions

2nd c Cholesteric liquid crystal mixture A, 0.1 g of 2,4,5-trimethylbenzoyldiphenylphosphine oxide and 0.04 g of cellulose acetobutyral and 0.1 g of polyoxyethylene stearyl ether were homogenized by intensive stirring. Then 1 ml of water was added and stirring was continued for a further 2 hours. A further ml of water was stirred in, a stable, flowable paste was obtained and, after a further ml of water, a low-viscosity emulsion was obtained.

Example 33

Analogously to Example 32, a mixture with 0.2 g of polyoxyethylene stearyl ether was prepared and 1 ml of water was added successively. After stirring, emulsions with characteristics similar to those described in Example 32 were formed, but with a slightly higher viscosity.