CA2587477A1 - Core/shell particles - Google Patents

Abstract

The invention relates to core-shell particles, the core of which is essentially solid with an essentially monodisperse size distribution, with a difference between the refractive index of the core material and the shell material. The core is made from a material which either does not flow or does so at a temperature above the flow temperature of the shell material and the shell is connected to the core by means of an intermediate layer, characterised in that the shell is made from a copolymer with at least one C<SUB>4</SUB>-C<SUB>8</SUB> alkylacrylate and at least one C<SUB>4</SUB>-C<SUB>8</SUB> alkyl- or -alkylarylmethacrylate as monomer component.

Description

Core/shell particles The invention relates to granules or dispersions comprising core/shell par-ticles, and to the core/shell particles and to processes for the preparation of the granules or dispersions or core/shell particles.

Patent Application WO 03/25035 discloses mouldings which essentially consist of core/shell particles whose shell forms a matrix and whose core is essentially solid and has an essentially monodisperse size distribution, where the shell is preferably strongly bonded to the core via an interlayer.
The refractive indices of the core material and the shell material differ here, causing the said optical effect, preferably opalescence. In a preferred em-bodiment in accordance with WO 03/25035, the core of the core/shell par-ticles consists of crosslinked polystyrene and the shell consists of a poly-acrylate, preferably polyethyl acrylate, polybutyl acrylate, polymethyl methacrylate and/or a copolymer thereof.

According to Patent Application DE 10204338, contrast materials, such as pigments, may additionally be introduced into mouldings of such core/shell particles. The incorporated contrast materials effect an increase in bright-ness, contrast and depth of the observed colour effects in these mouldings.
There is nevertheless a demand for core/shell particles for photonic mate-rials having optimised optical properties. In addition, the known core/shell particles are of only limited suitability for large-scale industrial processing by the usual methods in the polymer industry.

The object of the present invention was to provide core/shell particles which can be processed by large-scale industrial processing methods and/or have optimised optical properties.

P 04180 Ho CA 02587477 2007-05-15 The present invention therefore relates firstly to core/shell particles whose core is essentially solid and has an essentially monodisperse size distribu-tion, where there is a difference between the refractive indices of the core material and the shell material, and the core consists of a material which is either not flowable or becomes flowable at a temperature above the melting point of the shell material, and the shell is bonded to the core via an inter-layer, characterised in that the shell consists of a copolymer which com-prises at least one C4-C8-alkyl acrylate and at least one C4-C8-alkyl or -alkylaryl methacrylate as monomer units.

The present invention furthermore relates to granules comprising the core/shell particles according to the invention and optionally assistants and additives, and to dispersions comprising the core/shell particles according to the invention and at least one solvent or dispersion medium and option-ally dispersion aids, and to corresponding preparation processes.

In a preferred variant of the invention, the shell of the core/shell particles comprises from 10 to 70% by weight, preferably from 25 to 60% by weight and particularly preferably from 35 to 55% by weight of C4-C8-alkyl acrylate, from 10 to 80% by weight, preferably from 25 to 70% by weight and particularly preferably from 35 to 60% by weight of C4-C8-alkyl or -alkylaryl methacrylate and from 0.5 to 40% by weight, preferably from 1 to 30% by weight and particularly preferably from 5 to 20% by weight of methyl methacrylate, in each case based on the weight ratio of the monomer units, as monomer units.

It is particularly preferred here for the at least one C4-C8-alkyl acrylate to be selected from the group consisting of n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, n-propyl acrylate, n-pentyl acrylate, n-hexyl acrylate, n-octyl acrylate, where the at least one C4-C8-alkyl acrylate is preferably n-butyl acrylate.

P 04/180 Ho ' CA 02587477 2007-05-15 The at least one C4-C$-alkyl or -alkylaryl methacrylate is preferably selected from the group consisting of n-butyl methacrylate, isobutyl methacrylate, sec-butyl methacrylate, n-propyl methacrylate, n-pentyl methacrylate, n-hexyl methacrylate, cyclohexyl methacrylate, n-octyl methacrylate, benzyl methacrylate, where the at least one C4-C8-alkyl acrylate is preferably n-butyl methacrylate.

In accordance with the invention, the shell is very particularly preferably formed from a random copolymer, which is preferably built up from n-butyl acrylate, n-butyl methacrylate and methyl methacrylate.

In particular, the core/shell particles according to the invention have the following advantages here:
- Dispersions of the core/shell particles according to the invention are shear-stable. The dispersions can be conveyed by pumping. No unde-sired coagulation takes place.
- The particles are approximately odour-neutral. Compared with core/shell particles having an ethyl acrylate-containing shell, which tend towards a pungent odour, the complex purification of the products from residual monomers is thus superfluous in the preparation. In practice, the removal of the ethyl acrylate residual monomers by post-initiation and polymerisation of the residual monomers results in a significant im-pairment of the processing properties of the ethyl acrylate-containing core/shell particles. This impairment can be avoided with the particles according to the invention.
- In addition, mouldings made from the particles according to the inven-tion exhibit increased brightness of the colour effects.
- The mechanical load-bearing capacity of the mouldings which can be produced in accordance with the invention is improved compared with the prior art.

in a preferred embodiment of the invention, the interlayer is a layer of crosslinked or at least partially crosslinked polymers. The crosslinking of the interlayer here can take place via free radicals, for example induced by UV irradiation, or preferabiy via di- or oligofunctional monomers. Preferred interlayers in this embodiment comprise from 0.01 to 100% by weight, par-ticularly preferably from 0.25 to 10% by weight, of di- or oligofunctional monomers. Preferred di- or oligofunctional monomers are, in particular, isoprene and allyl methacrylate (ALMA). Such an interlayer of crosslinked or at least partially crosslinked polymers preferably has a thickness in the range from 10 to 20 nm. If the interlayer comes out thicker, the refractive index of the layer is selected so that it corresponds either to the refractive index of the core or to the refractive index of the shell.

If copolymers which, as described above, contain a crosslinkable monomer are employed as interlayer, the person skilled in the art will have absolutely no problems in suitably selecting corresponding copolymerisable mono-mers. For example, corresponding copolymerisable monomers can be selected from a so-called Q-e-scheme (cf. textbooks on macromolecular chemistry). Thus, monomers such as methyl methacrylate and methyl acrylate can preferably be polymerised with ALMA.

In another, likewise preferred embodiment of the present invention, the shell polymers are grafted directly onto the core via a corresponding func-tionalisation of the core. The surface functionalisation of the core forms the interlayer according to the invention. The type of surface functionalisation here depends principally on the material of the core. Silicon dioxide sur-faces, for example, can be suitably modified with silanes carrying corre-spondingly reactive end groups, such as epoxide functions or free double bonds. Other surface functionalisations, for example for metal oxides, may be titanates or organoaluminium compounds, each containing organic side chains with corresponding functions. In the case of polymeric cores, a sty-rene functionalised on the aromatic ring, such as bromostyrene, can, for P 04/180 Ho CA 02587477 2007-05-15 example, be employed for the surface modification. The grafting-on of the shell polymers can then be achieved via this functionalisation. In particular, the interlayer may also effect adhesion of the shell to the core via ionic interactions or complex bonds.
The core of the core/shell particles consists of a material which is either not flowable or becomes flowable at a temperature above the melting point of the shell material. This can be achieved through the use of polymeric materials having a correspondingly high glass transition temperature (Tg), preferably crosslinked polymers, or through the use of inorganic core mate-rials.

In a preferred variant of the invention, the core consists of an inorganic material, preferably a metal or semimetal or a metal chalcogenide or metal pnictide. For the purposes of the present invention, the term chalcogenides is applied to compounds in which an element from group 16 of the Periodic Table is the electronegative bonding partner; the term pnictides is applied to those in which an element from group 15 of the Periodic Table is the electronegative bonding partner.

Preferred cores consist of metal chalcogenides, preferably metal oxides, or metal pnictides, preferably nitrides or phosphides. For the purposes of these terms, the term metal is taken to mean all elements which can occur as electropositive partner compared with the counterions, such as the clas-sical metals from the sub-groups, or the main-group metals from the first and second main groups, but equally well all elements from the third main group, as well as silicon, germanium, tin, lead, phosphorus, arsenic, anti-mony and bismuth. Preferred metal chalcogenides and metal pnictides include, in particular, silicon dioxide, aluminium oxide, gallium nitride, boron nitride, aluminium nitride, silicon nitride and phosphorus nitride.

P 04/180 Ho' CA 02587477 2007-05-15 In a variant of the present invention, the starting material employed for the production of the core/shell particles according to the invention preferably comprises monodisperse cores of silicon dioxide, which can be obtained, for example, by the process described in US 4,911,903. The cores here are produced by hydrolytic polycondensation of tetraalkoxysilanes in an aqueous/ammoniacal medium, where firstly a sol of primary particles is produced, and the resultant Si02 particles are subsequently converted to the desired particle size by continuous, controlled, metered addition of tetraalkoxysilane. This process enables the production of monodisperse Si02 cores having mean particle diameters of between 0.05 and 10 pm with a standard deviation of 5%.

Preferred starting materials are furthermore Si02 cores which have been coated with (semi)metals or with metal oxides which are non-absorbent in the visible region, such as, for example, Ti02, Zr02, Zn02, Sn02 or AI203.
The production of Si02 cores coated with metal oxides is described in greater detail in, for example, US 5,846,310, DE 198 42 134 and DE 199 29 109.

Another starting material which can be empioyed comprises monodisperse cores of non-absorbent metal oxides, such as Ti02, Zr02, Zn02, Sn02 or AI203, or metal-oxide mixtures. Their production is described, for example, in EP 0 644 914. Furthermore, the process described in EP 0 216 278 for the production of monodisperse Si02 cores can be applied readily and with the same result to other oxides. Tetraethoxysilane, tetrabutoxytitanium, tetrapropoxyzirconium or mixtures thereof are added in one portion with vigorous mixing to a mixture of alcohol, water and ammonia, whose tem-perature is set precisely to from 30 to 40 C by means of a thermostat, and the resultant mixture is stirred vigorously for a further 20 seconds, during which a suspension of monodisperse cores in the nanometre range forms.
After a post-reaction time of from 1 to 2 hours, the cores are separated off in a conventional manner, for example by centrifugation, washed and dried.

P 04/180 Ho CA 02587477 2007-05-15 Suitable starting materials for the production of the core/shell particles according to the invention are furthermore also monodisperse cores of polymers which contain included particles, for example metal oxides. Mate-rials of this type are available, for example, from micro caps Entwicklungs-and Vertriebs GmbH in Rostock. Microencapsulations based on polyesters, polyamides and natural and modified carbohydrates are produced in accordance with customer-specific requirements.

It is furthermore possible to employ monodisperse cores of metal oxides which have been coated with organic materials, for example silanes. The monodisperse cores are dispersed in alcohols and modified with conven-tional organoalkoxysilanes. The silanisation of spherical oxide particles is also described in DE 43 16 814. The silanes preferably form the above-mentioned interlayer here.

For the intended use of the core/shell particles according to the invention for the production of mouldings, it is important that the shell material can be formed into a film, i.e. that it can be softened, viscoelastically plasticised or liquefied by simple measures to such an extent that the cores of the core/shell particles are at least able to form domains having a regular arrangement. The regularly arranged cores in the matrix formed by film formation of the shells of the core/shell particles form a diffraction grating, which causes interference phenomena and thus results in very interesting colour effects.

With regard to the possibility of varying the invention-relevant properties of the cores of the core/shell particles according to the invention as needed, however, it is often advantageous for the cores to comprise one or more polymers and/or copolymers (core polymers) or to consist of polymers of this type.

P 04/180 Ho CA 02587477 2007-05-15 Therefore, in a variant of the invention, the cores particularly preferably consist of organic homo- or copolymers, which are preferably crosslinked.
The cores preferably comprise a single polymer or copolymer. It is particu-larly preferred in accordance with the invention for the core to consist of crosslinked polystyrene or a copolymer of methyl methacrylate and styrene.
With the use of polymer substances as core material, the person skilled in the art gains the freedom to determine their relevant properties, such as, for example, their composition, the particle size, the mechanical data, the refractive index, the glass transition temperature, the melting point and the core:shell weight ratio and thus also the applicational properties of the core/shell particles, which ultimately also affect the properties of the mouldings produced therefrom.
Polymers and/or copolymers which may be present in the core material or of which it consists are high-molecular-weight compounds which conform to the specification given above for the core material. Both polymers and copolymers of polymerisable unsaturated monomers and polycondensates and copolycondensates of monomers containing at least two reactive groups, such as, for example, high-molecular-weight aliphatic, aliphatic/
aromatic or fully aromatic polyesters, polyamides, polycarbonates, poly-ureas and polyurethanes, but also amino and phenolic resins, such as, for example, melamine-formaldehyde, urea-formaldehyde and phenol-form-aidehyde condensates, are suitable.

For the preparation of epoxy resins, which are likewise suitable as core material, epoxide prepolymers, which are obtained, for example, by reac-tion of bisphenol A or other bisphenols, resorcinol, hydroquinone, hexane-diol or other aromatic or aliphatic diols or polyols, or phenol-formaldehyde condensates, or mixtures thereof with one another, with epichlorohydrin or P04/180Ho' CA 02587477 2007-05-15 other di- or polyepoxides, are usually mixed with further condensation-capable compounds directly or in solution and allowed to cure.

In a preferred variant of the invention, the polymers of the core material are advantageously crosslinked (co)polymers, since these usually only exhibit their glass transition at high temperatures. These crosslinked polymers may either already have been crosslinked during the polymerisation or poly-condensation or copolymerisation or copolycondensation or may have been post-crosslinked in a separate process step after the actual (co)polymerisation or (co)polycondensation.

With regard to the ability of the core/shell particles to be converted into mouldings, it is advantageous for the core:shell weight ratio to be in the range from 2:1 to 1:5, preferably in the range from 3:2 to 1:3 and particu-larly preferably in the range less than 1.2:1. In specific embodiments of the present invention, it is even preferred for the core:shell weight ratio to be less than 1:1, with a typical upper limit of the shell proportion being at a core:shell weight ratio of 2:3.

The core/shell particles according to the invention can be produced by various processes. The present invention furthermore relates to a preferred way of obtaining the particles. This is a process for the preparation of dis-persions of core/shell particles by a) surface treatment of monodisperse cores, and b) application of the shell comprising organic polymers to the treated cores.

In a process variant, the monodisperse cores are obtained by emulsion polymerisation in a step a).

In a preferred variant of the invention, a crosslinked polymeric interlayer, which preferably has reactive centres to which the shell can be covalently P 04/180 Ho CA 02587477 2007-05-15 bonded, is applied to the cores, preferably by emulsion polymerisation or by ATR polymerisation, in step b). ATR polymerisation here stands for atom transfer radical polymerisation, as described, for example, in K.
Matyjaszewski, Practical Atom Transfer Radical Polymerization, Polym.
Mater. Sci. Eng. 2001, 84. The encapsulation of inorganic materials by means of ATRP is described, for example, in T. Werne, T. E. Patten, Atom Transfer Radical Polymerization from Nanoparticles: A Tool for the Prepa-ration of Well-Defined Hybrid Nanostructures and for Understanding the Chemistry of Controlled/"Living" Radical Polymerization from Surfaces, J.
Am. Chem. Soc. 2001, 123, 7497-7505 and WO 00/11043. The perform-ance both of this method and of emulsion polymerisations is familiar to the person skilled in the art of polymer preparation and is described, for exam-ple, in the above-mentioned literature references.

Accordingly, a process for the preparation of dispersions in which the monodisperse cores are obtained by emulsion polymerisation in a step al), and a crosslinked polymeric interlayer, which preferably has reactive cen-tres to which the shell can be covalently bonded, is applied to the cores, preferably by emulsion polymerisation or by ATR polymerisation, in a step a2), is a preferred variant of the process according to the invention.

The liquid reaction medium in which the polymerisations or copolymerisa-tions can be carried out consists of the solvents, dispersion media or dilu-ents usually employed in polymerisations, in particular in emulsion polym-erisation processes. The choice here is made in such a way that the emul-sifiers employed for homogenisation of the core particles and shell precur-sors are able to develop adequate efficacy. Suitable liquid reaction media for carrying out the process according to the invention are aqueous media, in particular water.
Suitable_for initiation of the polymerisation are, for example, polymerisation initiators which decompose either thermally or photochemically, form free P 04/180 Ho CA 02587477 2007-05-15 radicals and thus initiate the polymerisation. Preferred thermally activatable polymerisation initiators here are those which decompose at between 20 and 180 C, in particular between 20 and 80 C. Particularly preferred poly-merisation initiators are peroxides, such as dibenzoyl peroxide, di-tert-butyl peroxide, peresters, percarbonates, perketals, hydroperoxides, but also inorganic peroxides, such as H202, salts of peroxosulfuric acid and peroxodisulfuric acid, azo compounds, alkylboron compounds, and hydro-carbons which decompose homolytically. The initiators and/or photoinitia-tors, which, depending on the requirements of the polymerised material, are employed in amounts of between 0.01 and 15% by weight, based on the polymerisable components, can be used individually or, in order to utilise advantageous synergistic effects, in combination with one another. In addition, use is made of redox systems, such as, for example, salts of peroxodisulfuric acid and peroxosulfuric acid in combination with low-valency sulfur compounds, particularly ammonium peroxodisulfate in com-bination with sodium dithionite.

Corresponding processes have also been described for the preparation of polycondensation products. Thus, it is possible for the starting materials for the preparation of polycondensation products to be dispersed in inert liq-uids and condensed, preferably with removal of low-molecular-weight reaction products, such as water or - for example on use of di(lower alkyl) dicarboxylates for the preparation of polyesters or polyamides - lower alkanols.
Polyaddition products are obtained analogously by reaction of compounds which contain at least two, preferably three, reactive groups, such as, for example, epoxide, cyanate, isocyanate or isothiocyanate groups, with com-pounds carrying complementary reactive groups. Thus, isocyanates react, for example, with alcohols to give urethanes, with amines to give urea deri-vatives, while epoxides react with these complementary groups to give hydroxyethers and hydroxylamines respectively. Like the polycondensa-P 04/180 No CA 02587477 2007-05-15 tions, polyaddition reactions can also advantageously be carried out in an inert solvent or dispersion medium.

It is also possible for aromatic, aliphatic or mixed aromatic/aliphatic poly-mers, for example polyesters, polyurethanes, polyamides, polyureas, poly-epoxides or also solution polymers, to be dispersed or emulsified (secon-dary dispersion) in a dispersion medium, such as, for example, in water, alcohols, tetrahydrofuran or hydrocarbons, and to be post-condensed, crosslinked and cured in this fine distribution.

The stable dispersions required for these polymerisation, polycondensation or polyaddition processes are generally prepared using dispersion aids besides the solvents or dispersion media.

The dispersion aids used are preferably water-soluble, high-molecular-weight organic compounds containing polar groups, such as polyvinyl-pyrrolidone, copolymers of vinyl propionate or acetate and vinylpyrrolidone, partially saponified copolymers of an acrylate and acrylonitrile, polyvinyl alcohols having different residual acetate contents, cellulose ethers, gela-tine, block copolymers, modified starch, low-molecular-weight polymers containing carboxyl and/or sulfonyl groups, or mixtures of these sub-stances, where the proportion of dispersion aid in the dispersion is pref-erably in the range from 0.01 to 10% by weight, particularly preferably in the range from 0.5 to 5% by weight.
Particularly preferred protective colloids are polyvinyl alcohols having a residual acetate content of less than 35 mol%, in particular from 5 to 39 mol%, and/or vinylpyrrolidone-vinyl propionate copolymers having a vinyl ester content of less than 35% by weight, in particular from 5 to 30%
by weight.

P 04/180 Ho ' CA 02587477 2007-05-15 It is possible to use nonionic or ionic emulsifiers, if desired also as a mix-ture. Preferred emulsifiers are ethoxylated or propoxylated, relatively long-chain alkanols or alkylphenols having different degrees of ethoxylation or propoxylation (for example adducts with from 0 to 50 mol of alkylene oxide) or neutralised, sulfated, sulfonated or phosphated derivatives thereof. Also particularly suitable are neutralised dialkylsulfosuccinic acid esters or alkyl-diphenyl oxide disulfonates, where the use of nonionic emulsifiers and in particular the use of ethoxylated alkylphenols is preferred. As an example thereof, mention may be made of the octylphenol ethoxylates available under the trade name TritonTM (Dow Chemicals).

Particularly advantageous are combinations of these emulsifiers with the above-mentioned protective colloids, since particularly finely divided dis-persions are obtained therewith. Dispersions comprising at least one non-ionic or ionic emulsifier and at least one protective colloid are therefore particularly preferred in accordance with the invention.

Special processes for the production of monodisperse polymer particles have also already been described in the literature (for example R.C.
Backus, R.C. Williams, J. Appi. Physics 19, p. 1186 (1948)) and can advan-tageously be employed, in particular, for the production of the cores. It need merely be ensured here that the above-mentioned particle sizes are observed. A further aim is the greatest possible uniformity of the polymers.
The particle size in particular can be set via the choice of suitable emulsifi-ers and/or protective colloids or corresponding amounts of these com-pounds.

Through the setting of the reaction conditions, such as temperature, pres-sure, reaction duration and use of suitable catalyst systems, which influ-ence the degree of polymerisation in a known manner, and the choice of the monomers employed for their preparation - in terms of type and pro-P04/180Ho' CA 02587477 2007-05-15 portion - the desired property combinations of the requisite polymers can be set specifically. The particle size can be set, for example, via the choice and amount of the initiators and other parameters, such as the reaction temperature. The corresponding setting of these parameters presents the person skilled in the art in the area of polymerisation with no difficulties at all.

In particular on use of inorganic cores, it may also be preferred for the core to be subjected to pre-treatment which enables bonding of the shell before the shell is polymerised on. This can usually consist in chemical functiona-lisation of the particle surface, as is known from the literature for a very wide variety of inorganic materials. It may particularly preferably involve application to the surface of chemical functions which, as reactive chain end, enable grafting-on of the shell polymers. Examples which may be mentioned in particular here are terminal double bonds, epoxy functions and polycondensable groups. The functionalisation of hydroxyl-carrying surfaces with polymers is disclosed, for example, in EP-A-337 144. Further methods for the modification of particle surfaces are well known to the per-son skilled in the art and are described, for example, in various textbooks, such as Unger, K.K., Porous Silica, Elsevier Scientific Publishing Company (1979).

The present invention furthermore relates to a process for the preparation of granules comprising core/shell particles in which a dispersion is dried and compounded.

The drying here can be carried out by means of conventionai methods, such as, for example, spray drying, fluidised-bed drying or freeze drying.

The granules according to the invention may, if it is technically advanta-geous, comprise assistants and additives here. They can serve for opti-P 04/180 Ho CA 02587477 2007-05-15 mum setting of the applicational data or properties desired or necessary for application and processing. Examples of assistants and/or additives of this type are antioxidants, UV stabilisers, biocides, plasticisers, film-formation assistants, flow-control agents, fillers, melting assistants, adhesives, release agents, application assistants, demoulding assistants and viscosity modifiers, for example thickeners.

Particularly recommended are additions of film-formation assistants and film modifiers based on compounds of the general formula HO-CnH2n-O-(CõH2ri-O)mH, in which n is a number from 2 to 4, preferably 2 or 3, and m is a number from 0 to 500. The number n can vary within the chain, and the various chain members can be incorporated in a random or blockwise dis-tribution. Examples of assistants of this type are ethylene glycol, propylene glycol, di-, tri- and tetraethylene glycol, di-, tri- and tetrapropylene glycol, polyethylene oxides, polypropylene oxide and ethylene oxide-propylene oxide copolymers having molecular weights up to about 15,000 and a ran-dom or block-like distribution of the ethylene oxide and propylene oxide groups.

If desired, organic or inorganic solvents, dispersion media or diluents, which, for example, extend the open time of the formulation, i.e. the time available for its application to substrates, waxes or hot-melt adhesives are also possible as additives.

If desired, stabilisers against UV radiation and weathering influences can also be added to the granules. Suitable for this purpose are, for example, derivatives of 2,4-dihydroxybenzophenone, derivatives of 2-cyano-3,3'-di-phenyl acrylate, derivatives of 2,2',4,4'-tetrahydroxybenzophenone, deriva-tives of o-hydroxyphenylbenzotriazole, salicylic acid esters, o-hydroxy-phenyl-s-triazines or sterically hindered amines. These substances may likewise be employed individually or in the form of a mixture.

P 04/180 Ho CA 02587477 2007-05-15 The total amount of assistants and/or additives is up to 40% by weight, preferably up to 20% by weight, particularly preferably up to 5% by weight, of the weight of the granules. Accordingly, the granules consist of at least 60% by weight, preferably at least 80% by weight and particularly prefera-bly at least 95% by weight, of core/shell particles.

The present invention furthermore relates to mouldings having an optical effect obtainable from the core/shell particles or granules described above, and to the use of core/shell particles or granules of this type for the pro-duction of mouldings.

For the purposes of the invention, the term optical effect is taken to mean both effects in the visible wavelength region of light and, for example, also effects in the UV or infrared region. It has recently become customary to refer to effects of this type in general as photonic effects. All these effects are optical effects for the purposes of the present invention, where, in a preferred embodiment, the effect is opalescence in the visible region. In the sense of a conventional definition of the term, the mouldings obtainable from the core/shell particles according to the invention are photonic crystals (cf. Nachrichten aus der Chemie; 49(9) September 2001; pp. 1018 - 1025).
In a preferred variant of the production of mouldings according to the invention, the temperature in step a) is at least 40 C, preferably at least 60 C, above the glass transition temperature of the shell of the core/shell particles. It has been found empirically that the flowability of the shell in this temperature range meets the requirements for economical production of the mouldings to a particular extent.

In a likewise preferred process variant which results in the mouldings according to the invention, the flowable core/shell particles are cooled P 04/180 Ho CA 02587477 2007-05-15 under the action of the mechanical force from b) to a temperature at which the shell is no longer flowable.

For the purposes of the present invention, the action of mechanical force can be the action of a force which occurs in the conventional processing steps of polymers. In preferred variants of the present invention, the action of mechanical force takes place either:
- by uniaxial pressing or - the action of force during an injection-moulding operation or - during a transfer moulding operation, - during (co)extrusion or - during a calendering operation or - during a blowing operation.

If the action of force takes place by uniaxial pressing, the mouldings ac-cording to the invention are preferably films. Films according to the inven-tion can preferably also be produced by calendering, film blowing or flat-film extrusion. The various ways of processing polymers under the action of mechanical forces are well known to the person skilled in the art and are revealed, for example, by the standard textbook Adolf Franck, "Kunststoff-Kompendium" [Plastics Compendium]; Vogel-Verlag; 1996.

If mouldings are produced by injection moulding, it is particularly preferred for the demoulding not to be carried out until the mould has cooled with the moulding present therein. When implemented industrially, it is advanta-geous here to employ moulds having a large cooling channel cross section, since the cooling can then take place in a shorter time. It has been found that cooling in the mould makes the colour effects according to the invention significantly more intense. It is assumed that better arrangement of the core/shell particles to form a lattice occurs during this uniform cooling P 04/180 Ho ' CA 02587477 2007-05-15 process. It is particularly advantageous here for the mould to be heated before the injection operation.

In order to achieve the optical or photonic effect according to the invention, it is desirable for the core/shell particles to have a mean particle diameter in the range from about 5 nm to about 2000 nm. It may be particularly pre-ferred here for the core/shell particles to have a mean particle diameter in the range from about 5 to 20 nm, preferably from 5 to 10 nm. In this case, the cores may be known as "quantum dots"; they exhibit the corresponding effects known from the literature. In order to achieve colour effects in the region of visible light, it is particularly advantageous for the core/shell par-ticles to have a mean particle diameter in the range about 50 - 500 nm.
Particular preference is given to the use of particles in the range 100 -500 nm since, in particles in this size range (depending on the refractive index contrast which can be achieved in the photonic structure), the reflec-tions of various wavelengths of visible light differ significantly from one another, and thus the opalescence which is particularly important for optical effects in the visible region occurs to a particularly pronounced extent in a very wide variety of colours. However, it is also preferred in a variant of the present invention to employ multiples of this preferred particle size, which then result in reflections corresponding to the higher orders and thus in a broad colour play.

A further crucial factor for the intensity of the observed effects is the differ-ence between the refractive indices of core and shell. Mouldings according to the invention preferably have a difference between the refractive indices of the core material and the shell material of at least 0.001, preferably at least 0.01 and particularly preferably at least 0.1.

In a particular embodiment of the invention, further nanoparticles are in-corporated into the matrix phase of the mouldings in addition to the cores of the core/shell particles. These particles are selected with respect to their P 04l180 Ho CA 02587477 2007-05-15 particle size in such a way that they fit into the cavities of the sphere packing of the cores and thus cause only little change in the arrangement of the cores. Through specific selection of corresponding materials and/or the particle size, it is firstly possible to modify the optical effects of the mouldings, for example to increase their intensity. Secondly, it is possible through incorporation of suitable "quantum dots" to functionalise the matrix correspondingly. Preferred materials are inorganic nanoparticles, in particu-lar nanoparticles of metals or of II-VI or Ill-V semiconductors or of materials which influence the magnetic/electrical (electronic) properties of the materials. Examples of preferred nanoparticles are noble metals, such as silver, goid and platinum, semiconductors or insulators, such as zinc chal-cogenides and cadmium chalcogenides, oxides, such as haematite, mag-netite or perovskite, or metal pnictides, for example gallium nitride, or mixed phases of these materials.

The precise mechanism which results in the uniform orientation of the core/shell particles in the mouldings according to the invention was hitherto unknown. However, it has been found that the action of a force is essential for the formation of the far-reaching order. It is assumed that the elasticity of the shell material under the processing conditions is crucial for the ordering process. The chain ends of the shell polymers generally attempt to adopt a coiled shape. If two particles come too close, the coils are com-pressed in accordance with the model concept, and repellent forces arise.
Since the shell-polymer chains of different particles also interact with one another, the polymer chains are stretched in accordance with the model if two particles move away from one another. Due to the attempts by the shell-polymer chains to re-adopt a coiled shape, a force arises which pulls the particles closer together again. In accordance with the model concept, the far-reaching order of the particles in the moulding is caused by the interplay of these forces.

P 04/180 Ho CA 02587477 2007-05-15 The invention furthermore relates to the use of mouldings according to the invention or of core/shell particles according to the invention for the prepa-ration of pigments. The pigments obtainable in this way are particularly suitable for use in paints, coatings, printing inks, plastics, ceramics, glasses and cosmetic formulations. For this purpose, they can also be employed mixed with commercially available pigments, for example inorganic and organic absorption pigments, metal-effect pigments and LC pigments. The particles according to the invention are furthermore also suitable for the preparation of pigment compositions and for the preparation of dry prepara-tions, such as, for example, granules. Pigment particles of this type preferably have a flake-form structure with an average particle size of 5 pm - 5 mm.

The pigments can be prepared, for example, by firstly producing a film from the core/shell particles, which may optionally be cured. The film can sub-sequently be comminuted in a suitable manner by cutting or crushing and, if desired, subsequent grinding to give pigments of suitable size. This op-eration can be carried out, for example, in a continuous belt process.

The pigment according to the invention can then be used for pigmenting surface coatings, powder coatings, paints, printing inks, plastics and cos-metic formulations, such as, for example, lipsticks, nail varnishes, cosmetic sticks, compact powders, make-up, shampoos and loose powders and gels.
The concentration of the pigment in the application system to be pigmented is generally between 0.1 and 70% by weight, preferably between 0.1 and 50% by weight and in particular between 1.0 and 20% by weight, based on the total solids content of the system. It is generally dependent on the spe-cific application. Plastics usually comprise the pigment according to the in-vention in amounts of from 0.01 to 50% by weight, preferably from 0.01 to 25% by weight, in particular from 0.1 to 7% by weight, based on the plastic P 04/180 Ho CA 02587477 2007-05-15 composition. In the coatings area, the pigment mixture is employed in amounts of from 0.1 to 30% by weight, preferably from 1 to 10% by weight, based on the coating dispersion. In the pigmentation of binder systems, for example for paints and printing inks for gravure printing, offset printing or screen printing, or as precursor for printing inks, for example in the form of highly pigmented pastes, granules, pellets, etc., pigment mixtures with spherical colorants, such as, for example, Ti02, carbon black, chromium oxide, iron oxide, and organic "coloured pigments", have proven particularly suitable. The pigment is generally incorporated into the printing ink in amounts of 2-35% by weight, preferably 5-25% by weight and in particular 8-20% by weight. Offset printing inks can comprise the pigment in amounts of up to 40% by weight or more. The precursors for printing inks, for exam-ple in the form of granules, as pellets, briquettes, etc., comprise up to 95%
by weight of the pigment according to the invention in addition to the binder and additives. The invention thus also relates to formulations which com-prise the pigment according to the invention.

The following examples are intended to explain the invention in greater detail without limiting it.

Examples Example 1: Preparation of dispersions of core/shell particles Weight [g] Notes Starting mixture 11.1 1,4-butanediol diacrylate (BDDA) 99.4 styrene 1.38 sodium disulfite in 40 ml of demineralised H20 4.2 dodecyl sulfate sodium salt TexaponTM K12, addition as (NaDS) 15% solution/27.95 g 6060 demineralised water Initiator 1 10.36 sodium peroxodisulfate 100% as 20.8% soln./49.8 ml 1.41 sodium disulfite 100% as 3.4% soln./41.5 mi stir for 15 min Solution I
221.7 1,4-butanediol diacrylate addition of solution 1 in (BDDA) 95 min 2011.3 styrene 4.25 potassium hydroxide 10.3 dodecyl sulfate sodium salt TexaponTM K12, addition as (NaDS) 15% solution/68.75 g 2945 demineralised water post-stirring time 10 min Initiator 2 2.66 sodium peroxodisulfate as 6.3% soln./42.2 ml post-stirring time 10 min P 04/180 Ho CA 02587477 2007-05-15 Solution 2 41.4 allyl methacrylate (AMA) addition of solution 2 in 20 min 372.8 methyl methacrylate (MMA) 2.1 dodecyl sulfate sodium salt TexaponTM K12, addition as (NaDS) 15% solution/13.78 g 538 demineralised water post-stirring time 20 min Solution 3 374.8 methyl methacrylate (MMA) addition of solution 3 over the course of 133 min 1761.79 butyl acrylate (n-BA) 1611.8 butyl methacrylate (n-BMA) 10.3 dodecyl sulfate sodium salt TexaponTM K12, addition as (NaDS) 15% solution/68.4 g 9.3 TritonTM X405 (70%) addition as 15% solution/
43.4 g 3633 demineralised water post-stirring time 30 min Post-stabilisation 279 g TritonTM X405 (70%) corr. to 195 g of pure TritonTM

TritonTM X405 is an octylphenol ethoxylate having an average number of 35 ethylene oxide recurring units (commercial product from The Dow Chemical Company).
Description of the procedure:

A water bath connected to a jacketed reactor is heated to 75 C.
6060 g of demineralised water and 27.95 g of TexaponTM K12 (15%) are introduced into a 20 I jacketed reactor fitted with impeller stirrer, and the reactor is flushed with nitrogen. 11.1 g of BDDA and 99.4 g of styrene are additionally added to the starting mixture.

P 041180 Ho CA 02587477 2007-05-15 The reactor is then heated with stirring. 1.38 g of NaHS are dissolved in 40 ml of demineralised water at about 32 C and added to the starting mix-ture. During this operation, the reactor is again flushed with nitrogen.
At 55 C - 58 C, 49.8 ml of NaPS (20.8%) and 41.5 mi of NaHS (3.4%) are injected into the reactor, and the reaction is initiated.
After 15 minutes, a monomer emulsion consisting of 221.7 g of BDDA, 2011.3 g of styrene, 68.75 g of TexaponTM K12 (15%), 4.25 g of potassium hydroxide and 2945 ml of demineralised water (flushed with N2) is metered in continuously over the course of 95 minutes via a membrane pump.
When the metered addition is complete, the mixture is stirred for a further 10 minutes.

42.2 mi of NaPS (6.3%) are then added. After 10 minutes, the second monomer mixture, consisting of 372.8 g of MMA, 41.4 g of AMA, 13.78 g of TexaponTM K12 (15%) and 538 g of demineralised water, is metered in continuously over the course of 20 minutes via a membrane pump.
After the metered addition, the mixture is stirred here for a further 20 min-utes.

After completion of the post-stirring time, the third monomer mixture is metered in continuously over the course of 135 minutes via a membrane pump. The third monomer mixture consists of 1761.79 g of n-BA, 374.8 g of MMA, 1611.8 g of n-BMA, 68.4 g of TexaponTM K12 (15%), 43.4 g of TritonTM X405 (15%) and 3633 g of demineralised water.

The process temperature during the addition of all three monomer mixtures is 75 C.

After completion of the metered addition, the mixture is stirred for a further 30 minutes and slowly cooled to RT. During the cooling, the dispersion is P 04/180 Ho CA 02587477 2007-05-15 slowly re-stabilised with 5% of TritonTM X405 (based on the solids content, i.e. 195 g of TritonTM X405, i.e. 279 g of 70% TritonTM X405 solution).

The dispersion is filtered through a nylon gauze at < 40 C.
The resultant particles have a shell polymer composition of 10% by weight of MMA, 47% by weight of n-BA and 43% by weight of n-BMA. Core/shell particles having varied weight ratios of the shell polymer constituents to one another can be obtained analogously by variation of the monomer pro-portions.

Example 2: Preparation of granules of the core/shell particles 3 kg of the core/shell particles from Example 1 are comminuted in a cutting mill (Rapid, model: 1528) with ice-cooling and subsequently compounded in a single-screw extruder (Plasti-Corder; Brabender; screw diameter 19 mm with 1-hole die (3 mm)). After a cooling zone, the compound is granulated in an A 90-5 granulator (Automatik).

Example 3a: Production of a film from core/shell particles 2 g of the granules from Example 2 are heated to a temperature of 120 C
without pressure in a Collin 300P press and pressed at a pressure of bar to give a film. After cooling to room temperature, the pressure is re-duced again.

P 04/180 Ho' Example 3b: Production of a film from corelshell particles 25 g of the granules from Example 2 are heated to a temperature of 150 C
without pressure in a press with cassette cooling system (Dr. Collin GmbH;
model: 300E) and pressed at a pressure of 250 bar to give a film. After cooling to room temperature, the pressure is reduced again after 8 minutes.
Example 4: Production of mouldings by injection moulding 0.2% by weight of release agent (Ceridust 3615; Clariant) is admixed with the granules from Example 2. The mixture is processed further using a Klockner Ferromatik 75 FX 75-2F injection-moulding machine, with the granules being injected into the mould, held at 80 C, at 900 bar and at a barrel temperature of 190 C, subsequently cooled in the mould and de-moulded at a mould temperature of 30 C, giving mouldings having an opti-cal effect which is dependent on the viewing angle.

Example 5: Production of a flat film (tape) Granules from Example 2 are processed in a flat-film machine consisting of a single-screw extruder (Gottfert; model: Extrusiometer; screw diameter 20 mm; L/D 25), a thickness-adjustable film mould (width 135 mm) and a heatable smoothing stack (Leistritz; roll diameter 15 mm; roll width 350 mm). A film tape having a width of 125 mm and a thickness of 1 mm is obtained.

Comparative Example A: Production of core/shell particles having a butyl acrylate shell P 04/180 Ho CA 02587477 2007-05-15 A starting mixture, held at 4 C, consisting of 217 g of water, 0.4 g of butanediol diacrylate (Merck, destabilised), 3.6 g of styrene (BASF, desta-bifised) and 80 mg of sodium dodecylsulfate (SDS; Merck) is introduced into a stirred-tank reactor, pre-heated to 75 C, fitted with propeller stirrer, argon protective-gas inlet and reflux condenser, and dispersed with vigor-ous stirring. Immediately after the introduction, the reaction is initiated by directly successive addition of 50 mg of sodium dithionite (Merck), 250 mg of ammonium peroxodisulfate (Merck) and a further 50 mg of sodium di-thionite (Merck), each dissolved in 5 g of water. After 10 min, a monomer emulsion comprising 6.6 g of butanediol diacrylate (Merck, destabilised), 59.4 g of styrene (BASF, destabilised), 0.3 g of SDS, 0.1 g of KOH and 90 g of water is metered in continuously over a period of 210 min. The reactor contents are stirred without further addition for 30 min. A second monomer emulsion comprising 3 g of allyl methacrylate (Merck, destabi-lised), 27 g of methyl methacrylate (BASF, destabilised), 0.15 g of SDS
(Merck) and 40 g of water is subsequently metered in continuously over a period of 90 min. The reactor contents are subsequently stirred without further addition for 30 min. A monomer emulsion comprising 130 g of butyl acrylate (Merck, destabilised), 139 g of water and 0.33 g of SDS (Merck) is subsequently metered in continuously over a period of 180 min. For virtu-ally complete reaction of the monomers, the mixture is subsequently stirred for a further 60 min. The core/shell particles are subsequently precipitated in 1 I of methanol, 1 I of dist. water is added, and the particles are filtered off with suction, dried and processed further as described in Examples 2 to 5.

Comparative Example B: Production of core/shell particles having a ethyl acrylate-butyl acrylate shell P 04/180 Ho CA 02587477 2007-05-15 A starting mixture, held at 4 C, consisting of 217 g of water, 0.4 g of butanediol diacrylate (Merck, destabilised), 3.6 g of styrene (BASF, desta-bilised) and 60 mg of sodium dodecylsulfate (SDS; Merck) is introduced into a stirred-tank reactor, pre-heated to 75 C, fitted with propeller stirrer, argon protective-gas inlet and reflux condenser, and dispersed with vigor-ous stirring. Immediately after the introduction, the reaction is initiated by directly successive addition of 50 mg of sodium dithionite (Merck), 300 mg of ammonium peroxodisulfate (Merck) and a further 50 mg of sodium di-thionite (Merck), each dissolved in 5 g of water. After 10 min, a monomer emulsion comprising 8.1 g of butanediol diacrylate (Merck, destabilised), 72.9 g of styrene (BASF, destabilised), 0.375 g of SDS, 0.1 g of KOH and 110 g of water is metered in continuously over a period of 150 min. The reactor contents are stirred without further addition for 30 min. A second monomer emulsion comprising 1.5 g of allyl methacrylate (Merck, destabi-lised), 13.5 g of methyl methacrylate (BASF, destabilised), 0.075 g of SDS
(Merck) and 20 g of water is subsequently metered in continuously over a period of 45 min. The reactor contents are subsequently stirred without further addition for 30 min. 50 mg of APS dissolved in 5 g of water are sub-sequently added. A monomer emulsion comprising 59.4 g of ethyl acrylate (MERCK, destabilised), 59.4 g of butyl acrylate, 1.2 g of acrylic acid, 120 g of water and 0.33 g of SDS (Merck) is subsequently metered in continu-ously over a period of 240 min. For virtually complete reaction of the monomers, the mixture is subsequently stirred for a further 60 min. The core/shell particles are subsequently precipitated in I I of methanol, I I of dist. water is added, and the particles are filtered off with suction and dried and processed further as described in Examples 2 to 5.

Example 6: Tensile and elongation experiments In a tensile experiment, standardised test specimens are clamped between two clamp jaws and stretched: length of the parallel section of the test P 04/180 Ho CA 02587477 2007-05-15 specimens about 20 mm; length of the measurement section: 25 mm; elon-gation measurement means: traverse with clamped length 30 mm; test speed: 20 mm/min; force measurement head: 1000 N; the preliminary force was 0.05 MPa. The force acting is based on the smallest cross sectional area of the test specimen and quoted as tensile stress.

Tensile Modulus Shell st of Elongation/ Yield Elongation a structure MnPgah/ elasticity/ % stress/MPa break/%
MPa 53.5% n-BMA, 36.5% n-BA, 4.00 24 57.6 3.77 174 10% MMA
43% n-BMA, 47% n-BA, 2.00 12 38.0 2.00 449 10% MMA
Comparative example 0.70 -2 50.6 0.68 648 90% EA 10%
MMA
It can be seen that the particles according to the invention have a greater modulus of elasticity and only deform at a higher yield stress.

Claims (26)

1) Core/shell particles whose core is essentially solid and has an essen-tially monodisperse size distribution, where there is a difference between the refractive indices of the core material and the shell mate-rial, and the core consists of a material which is either not flowable or becomes flowable at a temperature above the melting point of the shell material, and the shell is bonded to the core via an interlayer, characterised in that the shell consists of a copolymer which com-prises at least one C4-C8-alkyl acrylate and at least one C4-C8-alkyl or -alkylaryl methacrylate as monomer units.

2) Core/shell particles according to Claim 1, characterised in that the shell comprises (a) from 10 to 70% by weight, preferably from 25 to 60% by weight and particularly preferably from 35 to 55% by weight of C4-C8-alkyl acrylate, (b) from 10 to 80% by weight, preferably from 25 to 70% by weight and particularly preferably from 35 to 60% by weight of C4-C8-alkyl or -alkylaryl methacrylate, (c) from 0.5 to 40% by weight, preferably from 1 to 30% by weight and particularly preferably from 5 to 20% by weight of methyl methacrylate, in each case based on the weight ratio of the monomer units, as monomer units.

3) Core/shell particles according to at least one of Claims 1 or 2, charac-terised in that the at least one C4-C8-alkyl acrylate is selected from the group consisting of n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, n-propyl acrylate, n-pentyl acrylate, n-hexyl acrylate, n-octyl acrylate, where the at least one C4-C8-alkyl acrylate is preferably n-butyl acrylate.

4) Core/shell particles according to at least one of the preceding claims, characterised in that the at least one C4-C8-alkyl or -alkylaryl meth-acrylate is selected from the group consisting of n-butyl methacrylate, isobutyl methacrylate, sec-butyl methacrylate, n-propyl methacrylate, n-pentyl methacrylate, n-hexyl methacrylate, cyclohexyl methacrylate, n-octyl methacrylate, benzyl methacrylate, where the at least one C4-C8-alkyl acrylate is preferably n-butyl methacrylate.

5) Core/shell particles according to at least one of the preceding claims, characterised in that the shell is formed by a random copolymer, which is preferably built up from n-butyl acrylate, n-butyl methacrylate and methyl methacrylate.

6) Core/shell particles according to at least one of the preceding claims, characterised in that the shell is grafted onto the core via an at least partially crosslinked interlayer.

7) Core/shell particles according to at least one of the preceding claims, characterised in that the core consists of an organic polymer, which is preferably crosslinked, where the core particularly preferably consists of crosslinked polystyrene or a copolymer of methyl methacrylate and styrene.

8) Core/shell particles according to at least one of Claims 1 to 6, charac-terised in that the core consists of an inorganic material, preferably a metal or semimetal or a metal chalcogenide or metal pnictide, par-ticularly preferably silicon dioxide.

9) Core/shell particles according to at least one of the preceding claims, characterised in that the core/shell particles have a mean particle diameter in the range from about 5 nm to about 2000 nm, preferably in the range from about 5 to 20 nm or in the range 100 - 500 nm.

10) Core/shell particles according to at least one of the preceding claims, characterised in that the core:shell weight ratio is in the range from 2:1 to 1:5, preferably in the range from 3:2 to 1:3 and particularly preferably in the range less than 1.2:1.

11) Core/shell particles according to at least one of the preceding claims, characterised in that the difference between the refractive indices of the core material and the shell material is at least 0.001, preferably at least 0.01 and particularly preferably at least 0.1.

12) Granules comprising core/shell particles according to at least one of Claims 1 to 11 and optionally assistants and additives.

13) Granules according to Claim 12, characterised in that present as assistant and additive is at least one compound selected from the groups consisting of antioxidants, UV stabilisers, biocides, plasticis-ers, film-formation assistants, flow-control agents, fillers, melting assistants, adhesives, release agents, application assistants, de-moulding assistants, viscosity modifiers, such, as, for example, thick-eners.

14) Granules according to at least one of the preceding claims, character-ised in that assistants and additives are present in amounts of up to 40% by weight, preferably up to 20% by weight, particularly preferably up to 5% by weight, based on the weight of the granules.

15) Granules according to at least one of the preceding claims, character-ised in that present as assistant and additive is least one compound selected from the film-formation assistants and film modifiers, pref-erably based on compounds of the general formula HO-C n H2n-O-(C n H2n-O)m H, in which n is a number from 2 to 4, preferably 2 or 3, and m is a number from 0 to 500, where ethylene glycol, propylene glycol, di-, tri- and tetraethylene glycol, di-, tri- and tetrapropylene glycol, polyethylene oxides, polypropylene oxide and ethylene oxide-propylene oxide copolymers having molecular weights up to about 15,000 and a random or block-like distribution of the ethylene oxide and propylene oxide groups are particularly preferred.

16) Granules according to at least one of the preceding claims, character-ised in that present as assistant and additive is at least one compound selected from the stabilisers against UV radiation and weathering influences, preferably selected from the group consisting of the derivatives of 2,4-dihydroxybenzophenone, derivatives of 2-cyano-3,3'-diphenyl acrylate, derivatives of 2,2',4,4'-tetrahydroxybenzophe-none, derivatives of o-hydroxyphenylbenzotriazole, salicylates, o-hydroxyphenyl-s-triazines and sterically hindered amines, and mix-tures of these compounds.

17) Dispersion comprising (a) core/shell particles according to at least one of Claims 1 to 11 (b) at least one solvent or dispersion medium and (c) optionally dispersion aids.

18) Dispersion according to Claim 17, characterised in that the dispersion comprises at least one dispersion aid, where the dispersion aids employed are preferably water-soluble, high-molecular-weight organic compounds containing polar groups, such as polyvinylpyrrolidone, copolymers of vinyl propionate or acetate and vinylpyrrolidone, par-tially saponified copolymers of an acrylate and acrylonitrile, polyvinyl alcohols having different residual acetate contents, cellulose ethers, gelatine, block copolymers, modified starch, low-molecular-weight polymers containing carboxyl and/or sulfonyl groups, or mixtures of these substances, where the proportion of dispersion aid in the dis-persion is preferably in the range from 0.01 to 10% by weight, par-ticularly preferably in the range from 0.5 to 5% by weight.

19) Dispersion according to at least one of the preceding claims, charac-terised in that the dispersion comprises at least one protective colloid, where the protective colloid employed is preferably polyvinyl alcohols having a residual acetate content of less than 35% by weight, in par-ticular from 5 to 39 mol%, and/or vinylpyrrolidone-vinyl propionate co-polymers having a vinyl ester content of less than 35% by weight, in particular from 5 to 30% by weight.

20) Dispersion according to at least one of the preceding claims, charac-terised in that the dispersion comprises at least one nonionic or ionic emulsifier, where the emulsifier employed is preferably ethoxylated or propoxylated, relatively long-chain alkanols or alkylphenols having different degrees of ethoxylation or propoxylation (for example adducts with from 0 to 50 mol of alkylene oxide) or neutralised, sul-fated, sulfonated or phosphated derivatives thereof, in particular neu-tralised dialkylsulfosuccinic acid esters or alkyldiphenyl oxide disul-fonates, where the use of nonionic emulsifiers and in particular the use of ethoxylated alkylphenols is preferred.

21) Dispersion according to at least one of the preceding claims, charac-terised in that the dispersion comprises at least one nonionic or ionic emulsifier and at least one protective colloid.

22) Process for the preparation of dispersions according to at least one of Claims 17 to 21 by a) surface treatment of dispersed monodisperse cores, b) application of the shell comprising organic polymers to the treated cores from a).

23) Process for the preparation of dispersions according to Claim 22, characterised in that the monodisperse cores are obtained by emul-sion polymerisation in a step al), and a crosslinked polymeric inter-layer, which preferably has reactive centres to which the shell can be covalently bonded, is applied to the cores, preferably by emulsion polymerisation or by ATR polymerisation, in a step a2).

24) Process for the preparation of dispersions according to at least one of the preceding claims, characterised in that step b) is a grafting, pref-erably by emulsion polymerisation or ATR polymerisation.

25) Process for the preparation of dispersions according to at least one of Claims 22 or 23, characterised in that the inorganic core is subjected to pre-treatment which enables bonding of the shell before the shell is polymerised on.

26) Process for the preparation of granules comprising core/shell parti-cles, characterised in that a dispersion according to at least one of Claims 22 to 25 is dried and compounded.