Process for preparing a composition of pearlescent pigments

The invention relates to a method for preparing a Pearlescent pigment composition (preparation) as precursor containing a pearlescent ink.

Pearlescent pigment is usually dust or powder in Trade. For processing in the printing ink is the Pearlescent pigment with a binder solution and optionally mixed pressure conventional additives and Mixture to the printing process for the application in required viscosity adjusted. To achieve the for Pearlescent typical soft luster effect in the Ink is a uniform distribution and Orientation of the pearlescent pigment particles in the Binder required. In principle, at each processing Pearlescent pigments high shear forces should be avoided. Therefore must the pearlescent pigment prior to the actual dispersion process for the preparation of the ink over several hours with Solvents (so-called. "Swamps") pretreated. This Process is time-consuming and therefore costly. Despite the Pretreatment by "swamps" and stirring, the not always achieved desired uniform dispersion are thus not fully satisfy the printing.

EP 523567 A1 suggests the use of Pearlescent pigment for a water-ink before, to the formulation of the pigment slowly with the Binder is stirred. As an application method for these inks is the processing from the coating unit an offset machine or a flexo prefers. The pearlescent pigment is, inter alia, in the form of a titanium dioxide-coated mica flakes Pigments used which is available under the trade name Iriodin® is.

In EP 633 299A2 is the use of Pearlescent pigments for a low-viscosity offset printing ink described. The preparation of Offset printing ink preparation is carried out by dispersing of pearl luster pigment in the color with the aid of a Ball mill, sand mill or a roll mill (Three rolls), optionally at different Dispersion temperatures. The pigment particles are enveloped by the binder. The expiring of the devices Grinding pastes are then combined with additives to finished product added. This type of dispersion must because of the sensitivity of the pigment against mechanical shear forces with extraordinary care and slowly expire.

From DE 36 27 329 A1 is already a pearlescent pigment containing pigment preparation for coloring in particular, thermoplastic polymers are known in of the pearlescent pigment with a polyester / polyurethane block copolymer is coated with tertiary amino groups, to thereby obtain a good dispersibility. To this end, is the pearlescent pigment with slow motion with the said block copolymer wets to the pigment flakes not to destroy, if appropriate, a solvent removed and then a powdery free flowing Pearlescent pigment preparation obtained, optionally only to be screened. The pearlescent pigment preparation can immediately thereafter without further incorporated pretreatment in thermoplastic polymers be and has a good tolerance to these on. However, this preparation is not for printing inks suitable because the polyester / polyurethane block copolymer is not film-forming.

The object of the invention is therefore, for pearlescent provide printing inks in a mold, that thereby the actual production of the ink significantly is facilitated and simplified, and especially the expected print quality, that is an excellent is achieved pearlescent.

This object is achieved in that the pearlescent pigment by the method defined in claim 1 to a prepared particulate precursor of the ink becomes.

It has been found, surprisingly, that by Pre-wetting the pearlescent pigment particles with that Binder for the processing to printing ink is required or desired, a significantly more rapid and more uniform dispersion of the pigment particles in the during the actual production of the printing ink relied binder solution takes place. In addition to a Time savings and associated flexibility for the user, this leads to a significant improvement the desired pearlescence in print. Surprising This is because, given the presence of the Pearlescent pigment preparation in coarse particulate form a intensive mixing process is expected to provide a sufficiently uniform dispersion achieved. The decisive factor seems to be the pre-wetting the to be pigment particles with the corresponding binder, surprisingly, despite the transfer of the paste in a compact particulate remains. Obviously leads the occurring pressure or compression of the paste even a particularly intimate pre-wetting the Pigment particles with the binder.

As binders for pre-wetting the pearlescent pigment are all commonly used for printing inks in question coming binders or binder mixtures which, insofar as they are identical or at least compatible with the each for use next binder system of Ink are. Thus binder may on the basis of Cellulose, polyacrylate, polymethacrylate, alkyd, polyester, Polyphenol, urea, melamine, polyterpene, Polyvinyl, polyvinyl chloride, polyvinyl pyrrolidone resins, Polystyrenes, polyolefins, coumarone-indene, Hydrocarbon, ketone, aldehyde, aromatic-formaldehyde resins, Carbamic, sulfonamide, epoxy resins, Polyurethanes and / or natural oils or derivatives of Substances mentioned are used. A particularly good Redispersibility of pearlescent pigment preparation of the invention has been shown, when as binder Cellulose or cellulose compounds. Cellulose or cellulose compounds lead to visible an intense pre-wetting the pearlescent particles and thus result in an ink precursor which itself turn in an order compatible binder solution can rapidly disperse in the preparation of the ink. This is especially true for the pre-wetting with Cellulose compounds since these apparently one hand the Binding of the particles of the pearlescent pigment, on the other hand support the formation of the paste from which produced by compacting the preparation in particulate form becomes.

To the group of cellulose or cellulose compounds to be particularly for the novel process suitable include cellulose nitrate, alkyl cellulose, Hydroxicellulose, and Hydroxialkylcellulose Acetobutyrate.

The amount of binder used is not critical and is in the range of 0.5 to 45 wt .-%, preferably 2 to 15 Wt .-%.

However, of importance is obtained by adding solvent set for the viscosity of the mixture binder prior to forming the particles by compacting preparation to particulate form, because at too high a solvent content of Mixing the pearlescent pigments strongly for the separation of the Binder solution tend, while at a too high Viscosity wetting incomplete and the shaping of Particles is considerably more difficult.

The conversion of the pearlescent pigment paste in a compact Can according to different particle shape, to those skilled in common procedures carried out, namely by tabletting, Briquetting, pelletizing, granulating or Spray granulation. In all these cases, to the paste in a more or less viscous state, a pressure exercised that of the initially described pre-wetting Pigment particles supported with the binder. Accordingly, the particles have the form of tablets, Briquettes, pellets, granules, balls, sausages or other appropriate coarse-grained form. Especially preferably as compaction is a pressing or Extruding.

off When pressing the mixture or paste Pearlescent pigment and binder solution through a Perforated plate, the or either batchwise by piston takes place continuously by an extruder, arise Particles in sausage form. By appropriately Adjusting the viscosity of the mixture can be ensured be that the length of the particles by Cancel or tearing off on emergence from the perforated plate automatically regulated. The separating of the perforated plate However, exiting paste strands into particles may also known manner by mechanical action, eg., by circular severing knife done. The pelleting or Granulation is carried out in a known manner on pelletizing disks or in granulating and usually leads to Preparation spherical particles. The first in the way of particles produced pressing through a perforated plate can also subsequently by way of pelleting or granulating be reshaped. A tableting or Briquetting is done by pressing the paste in appropriate forms.

By subsequently to the preparation of the particles performance drying, the binder in Solvent contained largely removed, so that the Preparation particles on the one hand a sufficient show mechanical resistance to assist in the Handling and to keep their shape during transport, on the other hand in contact with a binder solution even the slightest mechanical action (agitation) quickly decompose and thereby disperse.

When the binder after removal of the solvent is still sufficiently viscous to compacting the paste to allow for particle shape can be thought even before the compacting by drying the solvent to remove from the paste. Optionally, through a Increasing the temperature of the paste the viscosity for Compaction is reduced.

The type of drying by compacting Prepared particles or the paste and characterized takes place driving solvent is in essentially depends on the type of used Solvent. Since most of the in question here Solvent, in particular in connection with the cellulose as a binder, below the softening point of the are binder volatile, the drying can be at elevated temperature perform. In this case, in the case of Drying the particles are thought the temperature to choose close to the softening point of the binder to characterized an at least in a surface layer of the particles incipient sintering of the pre-wetted with the binder to cause or coated pearlescent pigment particles. Thereby, the shape retention of the preparation particles for the handling and the transport time improved.

The present invention is also concerned with Pearlescent pigment based on mica, such. As muscovite, Biotite or synthetic mica, with a TiO₂- and or Fe₂O₃Coating. Optionally, moreover still more metal oxide layers of the series B, Al, Si, Cr, Sn, Zn, Zr or Ce be contained. It is also possible Pearlescent pigment with a coating of titanium suboxides, Titanium oxynitrides and nitrides, or mixtures thereof use. In addition to the metal oxide coating can also be a Based on color pigments or dyes on be the pearlescent pigment present. In addition, a Such coloristic refinement by mixing the Pearlescent pigments with coloring substances in the Pasting realized.

As part of the process of the invention can also be Mixtures of pearlescent and metallic pigments in the desired preparation prepared as shown has, that a certain proportion of metal pigments, the influence the pre-wetting is not affected with the binder. However, the proportion of metal pigments is no more than 20 % By weight of pearlescent pigment-share amount. As Metallic pigment are any in effect pigment sector common metals such as aluminum, copper, zinc, tin and their Alloys. Aluminum and gold bronze pigments are therefor prefers.