Pigment preparation and its use especially in printing inks

Details Pigment preparation and its use especially in printing inks Pigment preparation and its use especially in printing inks

2001-10-19

2004-03-09

Bell, Mark L. (Department: 1755)

Compositions: coating or plastic

Coating or plastic compositions

Marking

C106S415000, C106S417000, C106S403000, C106S481000

Reexamination Certificate

active

06702885

ABSTRACT:

SUMMARY OF THE INVENTION
The present invention relates to a pigment preparation comprising coated and/or uncoated SiO
2
flakes, one or more special-effect pigments and a phosphate compound and to its use, especially in printing inks.
Printing inks consist in general of binder, pigments or dyes and additives. In the case of printed products for printing packaging, labels and high-quality journals there is an ever-increasing requirement for luster to be given to the articles depicted.
Printing inks comprising luster pigments all have the disadvantage that they feature problems with print-run stability. They have a tendency to build up rapidly on the inking unit, printing plate and rubber cloth or else to sediment, so that a trouble-free print run or more than 10,000 sheets is generally not possible. A fundamental problem is the strong tendency of luster pigments, especially pearl luster pigments, owing to their plateletlike structure and the specific chemicophysical surface properties, to form agglomerates in the printing ink, the pigments lying atop one another in stacks and being difficult to separate owing to their strong adhesion. In addition, the luster imparted to such prints is generally unsatisfactory, owing to the inadequate amount of pigments transferred to the printed product. The ink becomes depleted in pigment on its path via inking unit, plate and rubber cloth. The pigment accumulates at exposed areas on the plate and cloth and leads to caking and piling.
In general, the only special-effect pigments which are suitable are those having a very small average particle size, since the particle size is critical for pigment transfer on printing. Pigments meeting this requirement exist only for pearly white and pastel shade colorations, but not for the gold, silver, bronze and copper tones which are of very great interest. To date, in the offset process, it has frequently proved impossible to produce such tones satisfactorily using special-effect pigments.
The use of platelet-shaped bismuth oxychloride pigments to obtain a pearl luster effect likewise does not lead to satisfactory results, since the pigment particles are highly sensitive to mechanical shear forces and are broken down in the ink nip.
The use of pearl luster pigments in printing inks for offset printing is known from DE 29 03 212, which discloses the pigmentation of a customary commercial oil-based print varnish with a preferably very finely divided pearl luster pigment. The offset print varnish preparation described therein is notable for the fact that the proportion of pearl luster pigments is very high, the upper limit of the pigment concentration in the suspension being set essentially only by the required flowability of the mixture. The proportion of pearl luster pigments in that case is in the range up to 65% by weight. Varnishes having such a high proportion of pigment are highly viscous and may need to be rendered more flowable with a diluent in order to be able to be processed in conventional offset printing machines. In contrast to the teaching to date, experiments in DE 29 03 212 have shown that the transfer of pigment from the inking unit to the substrate is disrupted at such high levels of pigmentation. There are print-run defects, such as piling and caking, meaning that the achievable pearl luster effect cannot be optimized solely by high pigmentation. Furthermore, the ink systems of DE 29 03 212 generally exhibit an inadequate dot definition, so that the ink systems described therein are restricted essentially to the printing of solid areas.
An object was therefore to find a pigment preparation, especially for printing inks, which achieves not only relatively high pigmentation of the printing ink but also satisfactory print-run properties.
It has surprisingly been found that the quality of the gloss effect and the amount of transferred pigment particles in a printing ink becomes optimum if use is made of a pigment preparation which comprises a mixture of uncoated SiO
2
flakes or SiO
2
flakes coated with one or more metal oxides, at least one special-effect pigment, and a phosphate compound.
The invention hence provides a pigment preparation comprising uncoated SiO
2
flakes or SiO
2
coated with one or more metal oxides, at least one special-effect pigment and a phosphate compound.
A component of the pigment preparation of the invention is the SiO
2
flakes, as described, for example, in WO 92/02351. SiO
2
flakes produced on a continuous belt in accordance with WO 93/08237 are based on a platelet-shaped, transparent, colored or colorless matrix and typically possess a thickness of about 0.1 to 5 &mgr;m, in particular about 0.2 o 2.0 &mgr;m. The length in the two other dimensions is typically about 1 to 250 &mgr;m, preferably about 2 to 100 &mgr;m and, more preferably, about 5 to 40 &mgr;m. The SiO
2
flakes may be covered with one or more metal layers and/or metal oxide layers. Examples of suitable metal oxides or metal oxide mixtures are, e.g., titanium dioxide, zirconium oxide, zinc oxide, iron oxides and/or chromium oxide, especially TiO
2
and/or Fe
2
O
3
. The matrix of the uncoated SiO
2
flakes may comprise a colorant; for example, a color-imparting metal oxide or an organic dye. The SiO
2
flakes can be coated, for example, as described in WO 93/08207 (wet chemical coating) or DE-A 196 14 637 (CVD process).
The outer metal oxide layer can also be a semitransparent layer of metal. Suitable metals for this are, for example, Cr, Ti, Mo, W, Al, Cu, Ag, Au and Ni. Preferred pigments have the following layer structure: SiO
2
flakes+metal+SiO
2
+metal oxide.
To induce special color effects, fine particles in the nanometer size range can be incorporated additionally into the metal oxide layers of higher or lower refractive index. Examples of suitable candidates are, e.g., finely divided TiO
2
or finely divided carbon (carbon black) with particle sizes of about 10 to 250 nm. A controlled influence can be exerted on luster and hiding power by virtue of the light-scattering properties of such particles.
The special effect pigment can be, e.g., a metal effect pigment, interference pigment, luster pigment, goniochromatic pigment, pearlescent pigment, a pigment which exhibits a special color or color-flop, etc. By metal effect pigment is meant a pigment giving a metallic coloration and appearance. By interference pigment is meant a pigment giving an interference effect. The special-effect pigment is preferably a customary commercial metal-effect pigment, such as, e.g., platelet-shaped iron oxide, aluminum flakes, e.g., Stapa-Alupaste® or Standart® from Eckart, special-effect pigments, such as Paliochrom® from BASF, and pearl luster pigments—mica flake pigments coated with metal oxides—obtainable, for example, from Merck KGaA, Darmstadt, under the trade name Iriodin®. The latter are known, for example, from the German Patents and Patent Applications 14 67 468, 19 59 998, 20 09 566, 22 14 545, 22 15 191, 22 44 298, 23 13 331, 25 22 572, 31 37 808, 31 37 809, 31 51 343, 31 51 354, 31 51 355, 32 11 602 and 32 53 017. Pearl luster pigments are preferably used for the printing ink. In particular, TiO
2
- and/or Fe
2
O
3
-coated mica pigments, glass flakes, ceramic flakes or synthetic platelets without a carrier are employed.
The pigment preparation can comprise a mixture of different special-effect pigments in order, for example, to achieve particular colorations. The ratio of SiO
2
flakes to special-effect pigment is about 10:1 to 1:10, preferably about 1:1 by weight.
In addition to the coated or uncoated SiO
2
flakes and the special-effect pigments, the pigment preparation of the invention may also include carbon black particles, flourescent pigments and/or organic color pigments, phyllosilicates, TiO
2
, CaCO
3
, CaSO
4
and/or kaolin. In that case the preparation preferably is about 30 to 100% by weight of SiO
2
flakes and special-effect pigments and about 0-70% by weight of carbon black particles, fluorescent pigments and/or color pigments.
A further component of the pigment

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