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

1999-12-23

2002-04-16

Green, Anthony (Department: 1755)

Compositions: coating or plastic

Materials or ingredients

Pigment, filler, or aggregate compositions, e.g., stone,...

C106S415000, C106S416000, C106S459000, C106S462000, C106S474000, C106S483000, C106S494000

Reexamination Certificate

active

06372036

ABSTRACT:

SUMMARY OF THE INVENTION
The present invention relates to a pigment preparation containing coated and/or uncoated Al
2
O
3
flakes, one or more special-effect pigments and a phosphate derivative 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 have partially 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 of 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 platelet like structure and the specific chemophysical 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, special-effect pigments which are most 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 in inadequate dot definition, so that the ink systems described therein are restricted essentially to the printing of solid areas.
The 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 consists essentially of a mixture consisting of uncoated Al
2
O
3
flakes or Al
2
O
3
flakes coated with one or more metals, metal oxides or metal sulfides, and at least one further special-effect pigment and a phosphate derivative.
The invention hence provides a pigment preparation essentially consisting of uncoated Al
2
O
3
flakes or Al
2
O
3
flakes coated with one or more metals, metal oxides or metal sulfides and at least one further special-effect pigment and a phosphate derivative.
The most important constituent of the pigment preparation of the invention are the Al
2
O
3
flakes, comprising platelet shaped Al
2
O
3
substrates. Coated aluminum oxide in a flaky form is commercially available for example from Merck KGaA under the tradename Xirallic®.
&agr;-Al
2
O
3
in the form of hexagonal flakes having a particle diameter greater than 10 &mgr;m and an aspect ratio (particle diameter/thickness) of 5-10 is known from JP 111239/1982 (Laid Open No.).
The Japanese Patent Publication No. 72527/1991 discloses &agr;-Al
2
O
3
in the form of flakes having an average particle diameter of 0.5-3 &mgr;m.
The JP 39362/1992 (Laid Open No.) describes Al
2
O
3
in the form of fine platy particles of a hexagonal crystal system with the plane perpendicular to the c axis grown into a plate.
Preferred Al
2
O
3
flakes are flakes composed of aluminum oxide (as a major constituent) and of titanium dioxide (as a minor constituent) which are known from U.S. Pat. No. 5,702,519. These Al
2
O
3
flakes are prepared from a uniform aqueous solution of water-soluble aluminum salt and titanium salt by hydrolysis with an alkali carbonate aqueous solution in the presence of an aqueous solution containing an alkali metal salt like alkali metal sulfate and phosphoric acid or phosphate, drying by evaporation (dehydration by heating), and molten salt treatment.
The Al
2
O
3
flakes can be provided with one or more metal oxide layers. Examples of suitable metal oxides or metal oxide mixtures are titanium dioxide, zirconium oxide, zinc oxide, iron oxides and/or chromium oxide, especially TiO
2
and/or Fe
2
O
3
. The Al
2
O
3
flakes can be coated in the same way like pearl luster pigments. Coating with a metal oxide or metal oxide mixture may be accomplished by any known methods, such as hydrolysis of a metal salt by heating or alkali, which deposits hydrated metal oxide, followed by calcination.
The Al
2
O
3
flakes can also be coated with one or more metal oxide layers of a metal or metal alloy selected e.g. from chromium, nickel, silver, bismuth, copper, tin or hastalloy.
Al
2
O
3
flakes can also be coated with sulfides e.g. of tungsten, molybdenum, cerium, lanthanum or rare earth elements.
The Al
2
O
3
flakes can be coated by wet chemical coating, by CVD or PVD processes. The metal coating on the Al
2
O
3
flakes functions to increase the hiding power of the pigment.
Special-effect pigments used are chosen preferably of customary commercial metal effect pigments, such as aluminum flakes, e.g. Stapa-Alupaste® from Eckart, special-effect pigments, such as Paliocrom® from BASF, BiOCl pigments, Liquid Crystal Polymer pigments (LCP), holographic pigments and pearl luster pigments—mica flakes coated with metal oxides—obtainable, for example, from Merck KGaA, Darmstadt, under the tradename 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 and multilayer pigments are preferably used for the printing inks. In particular, TiO
2
-and/or Fe
2
O
3
-coated SiO
2
-flakes, mica pigments, TiO
2
flakes, glass flakes, ceramic flakes or synthetic platelets without a carrier are employed.
The pigment preparation consists of a mixture of different special-effect pigments in order, for example, to achieve particular colorations. The ratio of Al
2
O
3
flakes to special-effect pigment is preferably from 10:1 to 1:10, more preferably 1:1.
In addition to the coated or uncoated

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