Pigment mixture

Details Pigment mixture Pigment mixture

1999-12-23

2001-09-25

Koslow, C. Melissa (Department: 1755)

Compositions: coating or plastic

Materials or ingredients

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

C106S417000, C106S442000, C106S483000

Reexamination Certificate

active

06294010

ABSTRACT:

SUMMARY OF THE INVENTION
The present invention relates to pigment mixtures containing at least two components, component A being Al
2
O
3
flakes coated with one or more metals, metal oxides and/or metal sulfides and component B being one or more functional pigments such as electrically conductive pigments, magnetic pigments, IR-reflecting pigments or lasermarkable pigments and to their use in varnishes, paints, printing inks, plastics and powder coatings.
For various areas of application, use is made nowadays of electrically conductive pigments with which it is possible, for example, to produce antistatic coatings for electronic equipment, antistatic floor coverings, antistatic finishes for explosion-protected areas, or electrically conductive primers for the painting of plastics. Magnetic pigments can be used, for example, for magnetic coatings and IR-reflective pigments are applied, for example, for agricultural films. Other functional pigments are of interest as well. Functional pigments are all pigments for which physical properties other than the optical properties have the highest priority. Examples are electrically conductive pigments, magnetic pigments, IR-reflective pigments, or lasermarkable pigments.
To produce dark conductive pigments, use is currently made of carbon black, graphite and nickel-coated graphite, and to produce light-colored pigments, use is made of metal platelets and mixed oxides, such as antimony-doped tin oxide, for example. These mixed oxides can be in the form in which they have been deposited on carriers, examples being mica, SiO
2
, glass or barium sulfate.
However, owing to their high light absorption in the visible spectral range, carbon black and graphite cannot be used for transparent, pale or colored coatings. A further problem is the strong absorption in the IR range, which leads to the frequently unwanted heating of the coated articles on exposure to sunlight, for example.
Metal platelets have the disadvantage that they are susceptible to corrosion and are non-transparent.
The inorganic oxides or mixed oxides employed to date, in the form of platelets with mica, for example, as carrier material, or in a form in which the dimensions in the three spatial directions are approximately equal, such as antimony-doped tin oxide without a carrier, require, as a result of their geometric form, relatively high use concentrations in order to exhibit a distinct effect.
The application of an additional layer to the pigment, however, implies a considerable additional expense in production and makes the product more expensive. In addition, the pigment has conductivity values which do not satisfy the high requirements.
In order to improve the conductivity of polymeric systems, such as plastics, paints or printing inks, for example, it is known from DE-A 42 12 950 to employ a pigment consisting of a component A, which consists of one or more conductive, platelet-shaped pigments, and a component B, which comprises one or more conductive, non-platelet-shaped pigments.
It has now surprisingly been found that a pigment mixture comprising coated Al
2
O
3
flakes in combination with electrically conductive pigments has similar conductive properties as the conductive pigments alone together with a very attractive coloristic depth and glitter effect. Pigment mixtures of Al
2
O
3
flake pigments with other functional pigments as magnetic or IR-reflective pigments lead to very effective combinations of coloristic and functional effects, too.
The invention hence provides a pigment mixture consisting of at least two components, component A and component B. Component A comprises Al
2
O
3
flakes coated with one or more metals, metal oxides and/or metal sulfides. The Al
2
O
3
flakes comprise platelet shaped Al
2
O
3
substrates. Component B comprises one or more functional pigments as such as electrically conductive pigments, laser-markable pigments, particularly for the laser marking of paper or plastics, magnetic pigments or pigments with IR reflecting properties. The invention also contemplates the use of the pigments of the invention in formulations such as, for example, varnishes, paints, printing inks, plastics and powder coatings.
The invention likewise provides the formulations, such as paints, varnishes, powder coating materials, printing inks, plastics and agricultural films, which comprise the pigment mixture of the invention.
The coated Al
2
O
3
flakes can be mixed in any proportion with the functional pigments. The preferred ratio of component A to component B is from 1:10 to 10:1, in particular from 1:2 to 2:1.
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 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 are coated with one or more metal oxide layers. Examples of suitable metal oxides or metal oxide mixtures are titanium dioxide, zirconium oxide, zinc oxide, iron oxide (Fe
2
O
3
and/or Fe
3
O
4
) and/or chromium oxide, especially TiO
2
and/or Fe
2
O
3
as described in U.S. Pat. No. 5,702,519. Coating of the Al
2
O
3
flakes with one ore more metal oxides may be accomplished by any known method such as hydrolysis of a metal salt by heating or alkali, which deposits hydrated metal oxide, followed by calcination.
Al
2
O
3
flakes can also be coated with one or more layers of a metal or metal alloy selected from chromium, nickel, silver, bismuth, copper, tin or hastalloy.
Al
2
O
3
flakes coated with a metal sulfide are coated with, for example, sulfides of tungsten, cerium, molybdenum, 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.
The effect of component B shall be demonstrated using the example of conductive pigments. By the conductive pigments of component B are understood all pigments known to the skilled worker and comprising platelet-shaped, acicular or fiber-like carrier materials, such as mica, glass flakes, SiO
2
flakes, ceramic platelets, glass fibers, alumina fibers or titanium dioxide fibers that are coated with a conductive layer. It is also possible to use a carrier-free conductive pigment. Preferred conductive pigments of the invention have a powder resistance of less than about 10 kg ohm cm.
Also suitable in principle are carbon fibers, although in this case no additional conductive coatings are necessary since the fibers already possess sufficient conductivity. By acicular, fiber-like particles are meant those having a length-to-diameter ratio of more than 5. Suitable platelet-shaped pigments are known, for example, from EP 0 373 575.
The invention additionally provides paints, printing inks, plastics or powder coating materials that are pigmented with the pigment mixture of the invention. The proportion of the pigment mixture therein is from 1 to 80% by weight, preferably more than 2% by weight, based on the overall solid content of the system in which it is employed.
As a conductive laye

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