Process for preparing a composition of pearlescent pigments

0001The invention relates to a process for the production A pearlescent pigment preparation (preparation) As a precursor for a pearlescent pigment Printing ink.

0002Pearlescent pigment is usually dust or In powder form. For processing in the The pearlescent pigment is dyed with a binder solution And optionally customary additives Mixed and the mixture applied to the application In the printing process. To achieve the typical pearlescent pigment Soft luster effect also in the printing ink is one As uniform distribution and orientation as possible Pearlescent pigment particles in the binder. In principle, every pearlescent pigment is processed High shear forces. Therefore, The pearlescent pigment before the actual dispersion process For producing the printing ink over several Hours with solvent. "Swamp"). This process is time-consuming and costly. Despite the pre-treatment by "swamp" And stirring can provide the desired uniform dispersion Not always be achieved and thereby also The pressure does not fully satisfy.

0003EP 523 567 A1 proposes the use Of pearlescent pigment for a water - thinnable Ink, for the formulation of the pigment Is slowly stirred with the binder. As an application method For these printing inks is the processing From the coating unit of an offset machine or from A flexographic printing unit. The pearlescent pigment Is inter alia in the form of a titanium dioxide coated Glow dome pigments used under Of the Iriodin® brand.

0004EP 633 299 A2 discloses the use of Pearlescent pigments for a low-viscosity offset printing ink Described. Production of offset printing ink preparation Is carried out by dispersing Of the pearlescent pigment in color by means of a ball mill, Sand mill or a roller chair (three rollers), Optionally at different dispersing temperatures. The pigment particles are thereby removed By the binder. The outgoing from the devices Grinding pastes are then mixed with the additives To the finished product. Also this kind of Dispersing must be due to the sensitivity of the Pigment particles against mechanical shearing forces exceptionally Carefully and slowly.

0005A pearlescent pigment is already known from DE 36 27 329 A1 Containing pigment preparation for coloring Of thermoplastics in particular In which the pearlescent pigment is coated with a polyester / polyurethane block copolymer With tertiary amino groups To thereby obtain good dispersibility to achieve. The pearlescent pigment is used for this purpose Under slow motion with the said Block copolymer does not wet to the pigment leaflets If necessary, a solvent is removed And then a powdered free-flowing Pearlescent pigment preparation obtained, if appropriate Only to be screened. The pearlescent pigment preparation Can be immediately followed without Further pretreatment into thermoplastic polymers And has a good compatibility with them on. However, this preparation is for printing inks Not suitable because the polyester / polyurethane block copolymer Is not film-forming.

0006It is therefore an object of the invention to provide pearlescent pigments For printing inks in a mold, That thereby the actual production of the printing ink Is considerably facilitated and simplified, and above all The expected print quality, ie, an excellent print quality Pearlescent effect is achieved.

0007This object is achieved by the fact that the A pearlescent pigment as defined in claim 1 Process for a particulate precursor of the Printing ink.

0008It has been surprisingly shown that By pre-wetting the pearlescent pigment particles With the binder used for the processing to be processed Printing ink is required or desired, a Considerably faster and more uniform dispersion Of the pigment particles in the form shown in FIG Preparation of the printing ink . Beside a time saving and Related flexibility for the user This leads to a clear improvement of the desired Pearl luster in print. This is surprising Therefore, because of the presence of the pearlescent pigment preparation In coarse particle form a more intense Mixing is expected to be a sufficient Uniform dispersion. Crucial The prewetting of the pigment particles seems to be the case With the corresponding binder, which Surprisingly despite transferring the paste into a Compact particle shape. Obviously The resulting compression or compression occurs Of the paste even to a particularly intimate prewetting Of the pigment particles with the binder.

0009As a binder for pre-wetting the pearlescent pigment All commonly used for printing inks Suitable binders or binder mixtures In so far as they are the same or at least Compatible with the respectively used Binder system of the printing ink. Thus, Binders based on cellulose, polyacrylate-polymethacrylate, Alkyd, polyester, polyphenol, Urea, melamine, polyterpene, polyvinyl, polyvinyl chloride, Polyvinylpyrrolidone resins, polystyrenes, polyolefins, Cumarone-indene, hydrocarbyl, ketone, Aldehyde, aromatic-formaldehyde resins, carbamic acid, Sulfonamide, epoxy resins, polyurethanes And / or natural oils or derivatives thereof Substances. One of them Good redispersibility of the invention Pearlescent pigment preparation has been shown, if As binder cellulose or cellulose compounds Can be used. Cellulose or cellulose compounds Clearly lead to an intensive prewetting Of the pearlescent pigment particles and thus result Printing ink precursor, which in turn is in one Compatible binder solution during manufacture Of the printing ink can be rapidly dispersed. this applies Especially for pre-wetting with cellulose compounds Since this, on the one hand, the binding of the The particles of the pearlescent pigment, on the other hand the Forming the paste, from the compacting The preparation is produced in particle form.

0010To the group of the cellulose or cellulose compounds, Which is particularly suitable for the invention Methods include cellulose nitrate, Alkylcellulose, hydroxicellulose, hydroxyalkylcellulose And cellulose acetobutyrate.

0011The amount of binder used is not Is critical and is in the range of 0.5 to 45% by weight, preferably 2 to 15% by weight.

0012Of importance, however, is the addition By weight of solvent for the binder Of the mixture before forming the preparation particles By compacting to the particle shape, since High solvent content of the mixture is the pearlescent pigment Strong for separation from the binder solution While the viscosity is too high Incomplete and the formation of particles Is considerably more difficult.

0013The transfer of the pearlescent pigment paste Into a compact particle shape can be determined according to different, The skilled worker, Namely by tabletting, briquetting, pelleting, Granulating or spray granulating. In all these cases Is applied to the paste in a more or less viscous State, a pressure is applied which corresponds to the beginning Described prewetting of the pigment particles With the binder. Correspondingly The particles take the form of tablets, briquettes, pellets, Granules, balls, sausages or any other appropriate Coarse-grained form. Particularly preferred As a compacting operation is a pressing or extrusion.

0014When the mixture or paste is pressed From pearlescent pigment and binder solution through a Perforated plate, either batchwise by means of flasks Or continuously through an extruder, Particles are formed in sausage form. Through the appropriate Adjust the viscosity of the mixture It can be ensured that the length of the particles Break or tear when exiting From the perforated plate self-regulating. The cutting Of the paste strands emerging from the perforated plate However, particles can also be formed in the known manner by means of Mechanical influence, eg by circulating Cutters. Pelleting or granulating Is carried out in a known manner on pelletizing plates or In granulating containers and usually leads to spherical Preparation particles. The first in the way Of the particles produced by a perforated plate Can additionally be carried out by pelleting Or granulating. On Tableting or briquetting is carried out by pressing the Paste in appropriate forms.

0015Through the subsequent shaping of the Preparation particles, this is achieved in the Binders are largely removed, So that the preparation particles on the one hand are sufficient Mechanical resistance During handling and transport On the other hand, in contact with a binder solution Even with minimal mechanical action (Stirring) rapidly disintegrate and thereby disperse.

0016When the binder after removal Of the solvent is still sufficiently viscous to remove the Compacting the paste to the particle shape, Can be thought of even before compacting To remove the solvent from the paste by drying. If desired, by a temperature increase Of the paste the viscosity for the compacting process be reduced.

0017The type of drying of the compacting And the paste, and the like Removal of the solvent is carried out in the Depending on the type of Solvent. Since most of the ones in question here Solvents, in particular in combination with Of the cellulose as a binder, under the softening point Of the binder are volatile, drying can be carried out At elevated temperature. It can be In the case of drying the particles, The temperature close to the softening point of the By weight of binder, to thereby form at least one A sintering layer beginning with a boundary layer of the particles Which pre-wetted or coated with the binder Pearlescent pigment particles. In this way The dimensional stability of the preparation particles for The handling and the duration of the transport.

0018The present invention is also concerned with Pearlescent pigment based on mica, such as, for example, muscovite, Biotite or synthetic mica, with a TiO₂and or Fe₂O₃Coating. If desired, In addition, further metal oxide layers of the Series B, Al, Si, Cr, Sn, Zn, Zr or Ce. It is also possible to use pearlescent pigment with a coating Of titanium suboxides, titanium oxynitrides and titanium nitrides Or mixtures thereof. In addition to the metal oxide coating, a Use of coloring pigments or dyes On the pearlescent pigment. also Is such a colorist configuration Mixing the pearlescent pigments with Substances can be realized during adaptation.

0019Within the scope of the inventive method It is also possible to use mixtures of pearlescent pigments And metal pigments in the desired preparation Since it has been shown that a certain Proportion of metal pigments influence the prewetting With the binder. However, The proportion of metal pigments should be no more than 20% by weight of the pearlescent pigment fraction. Suitable as a metal pigment are all in the effect pigment sector Common metals such as aluminum, copper, zinc, tin And their alloys. Aluminum and gold bronze pigments Are preferred for this purpose.