Conductive pigments

Details Conductive pigments Conductive pigments

1999-03-17

2001-04-24

Green, Anthony (Department: 1755)

Compositions: coating or plastic

Materials or ingredients

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

C106S415000, C106S461000, C106S462000, C106S482000, C252S520100, C428S403000, C428S404000, C428S406000

Reexamination Certificate

active

06221144

ABSTRACT:

The invention relates to electrically conductive pigments having a tin oxide layer doped with fluorine and phosphorus as a conductive layer on a substrate.
BACKGROUND OF THE INVENTION
In many sectors of industry there is a need for conductive pigments which can be used, for example, to produce plastics, lacquers, coatings or fibers or the like which are electrically conductive or antistatic or which screen against electromagnetic waves. Conductive carbon black is employed for this purpose in large amounts and yet because of its high light absorption cannot be used for pale or colored coatings. A further disadvantage is the strong absorption of carbon black in the IR region, which in the case, for example, of solar irradiation leads to frequently unwanted warming of the coated articles.
For pale conductive coatings, therefore, the use of doped metal oxides, especially antimony-doped tin oxide, is on the increase.
U.S. Pat. No. 5,472,640 describes conductive platelet-shaped pigments: a platelet-shaped substrate coated with one or more metal oxide layers is coated with a conductive layer of antimony-doped tin oxide, with a thin SiO
2
layer disposed between the conductive layer and the metal oxide layer.
U.S. Pat. No. 5,350,448 discloses a pale, electrically conductive pigment consisting of a platelet-shaped substrate and halogen-doped tin and/or titanium dioxide as the conductive layer. The specific resistance of the pigment is given as less than 25 k&OHgr;cm.
DE 44 35 301 describes electrically conductive pigments having a phosphorus-doped tin oxide layer as a conductive layer on a substrate. The specific resistance of the pigments is given as less than 10 k&OHgr;cm.
The pale conductive pigments of the prior art have levels of electrical conductivity which fail to satisfy the stringent requirements of certain conductive coatings.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide pale conductive pigments having better conductivity.
This object is achieved in accordance with the invention by pale, conductive pigments in which a substrate is coated with a conductive layer and which are characterized in that the layer consists of a phosphorus- and/or fluorine-doped tin oxide layer. It is possible for an interlayer to be disposed between the substrate and the conductive layer.
This object is further achieved in accordance with the invention by a process for preparing the pigments of the invention by suspending the substrate in water and metering in a solution of a hydrolyzable tin salt, the aqueous solution of a phosphorus compound and/or the aqueous solution of a fluoride, with the pH of the substrate suspension being kept constant within a range from 1 to 5 by simultaneous addition of acid or base, and separating off the coated substrate, washing it, drying it and calcining it in the absence of oxygen at temperatures from 400 to 1100° C.
This object is further achieved in accordance with the invention by a process for preparing the pigments of the invention by suspending the substrate in water and metering in the aqueous solution of a silicate, with the pH being held constant within a range from 4 to 10 by simultaneous addition of acid, and then metering in a solution of a hydrolyzable tin salt, the aqueous solution of a phosphorus compound and/or the aqueous solution of a fluoride, the pH of the substrate suspension being held constant within a range from 1 to 5 by simultaneous addition of acid or base, and separating off the coated substrate, washing it, drying it and calcining it in the absence of oxygen at temperatures from 400 to 1100° C.
This object is additionally achieved, in accordance with the invention, by a process for preparing the pigments of the invention by suspending the substrate in water and, following addition of a complexing agent, metering in a barium salt solution, with the pH being held constant within a range from 0 to 5 by simultaneous metered addition of dilute sulfuric acid and sodium sulfate, and then adding a solution of a hydrolyzable tin salt, the aqueous solution of a phosphorus compound and the aqueous solution of a fluoride, the pH of the substrate suspension being held constant within a range from 1 to 5 by simultaneous addition of acids or base, and separating off the coated substrate, washing it, drying it and calcining it in the absence of oxygen at temperatures from 400 to 1100° C.
Upon further study of the specification and appended claims, further objects and advantages of this invention will become apparent to those skilled in the art.
The invention additionally provides for the use of the pigments of the invention for pigmenting paints, printing inks, plastics, glazes for ceramics, and glasses and cosmetics. For these purposes they can also be employed as mixtures with commercially customary pigments, examples being organic and inorganic absorption pigments, metal effect pigments and LCP pigments.
Both platelet-shaped and spherical particles or mixtures thereof can be used as substrates. All known platelet-shaped substrate materials, such as metals, metal oxides, mica pigments and synthetic platelets, can be coated by the process of the invention and may already be coated with metal oxides. Examples of these materials are natural or synthetic mica, other phyllosilicates such as talc, kaolin or sericite, or other, comparable materials such as platelet-shaped iron oxide, aluminum flakes, bismuth oxychloride, or SiO
2
, glass or synthetic ceramic flakes.
Particularly preferred substrates are mica and platelet-shaped pigments and also SiO
2
flakes prepared in accordance with the International Application WO 93/08237. They consist of a transparent, inorganic platelet-shaped matrix, preferably silica, which may include an insoluble colorant. If, say, a highly transparent conductive pigment is to be prepared, a platelet-shaped substrate material is used whose matrix consists solely of silica. These conductive pigments are particularly suitable for producing electrically conductive clearcoats or transparent electrode layers.
Alternatively, if the requirement is for a pale conductive pigment of high hiding power, insoluble colorants, examples of which are titanium dioxide particles, are incorporated into the transparent matrix. The advantage of this preferred substrate material is that a substrate material which is itself of high hiding power can be used to prepare the pigment of the invention.
Since there is no need for high forces in the process, it is also outstandingly suited to the coating of pearl luster pigments. All customary pearl luster pigments can be used, such as micas coated with colored or colorless metal oxides, such as TiO
2
, Fe
2
O
3
, SnO
2
, Cr
2
O
3
, ZnO and other metal oxides, alone or in combination in one uniform layer or in successive layers. These pigments are known, for example, from the German patents and patent applications 14 67 468, 19 59 998, 20 09 566, 2 14 545, 22 15 191, 2 44 298, 23 13 331, 25 22 572, 32 11 602 and 32 35 017 and are obtainable commercially, for example under the trade name Iriodin® from the MERCK KGaA, Darmstadt.
The spherical particles may consist, for example, of SiO
2
or metal oxides, such as Fe
2
O3, TiO
2
, MgTiO
3
, CaTiO
3
, BaTiO
3
, SrTiO
3
, Al
2
O
3
or BaSO
4
, CaSO
4
or CaCO
3.
The particles preferably have an average diameter of less than 200 &mgr;m and, in particular, not more than 50 &mgr;m. Platelet-shaped substrates preferably have an extent in the main dimension of less than 500 &mgr;m and, in particular, less than 250 &mgr;m and their thickness preferably is less than 10 &mgr;m, preferably not more than 5 &mgr;m and, in particular, in the range 0.01-1 &mgr;m. The ratio of the extent in the main dimension to the thickness (aspect ratio) of the platelet-shaped substrates is more than 3 and, in particular more than 5.
The substrates to be coated may also consist of a mixture of platelet-shaped and spherical particles, in which case the ratio of platelet-shaped to spherical particles is preferably within the range from 80:20 to 20:80 and, in par

Affiliated with

Also associated with

Rating

Conductive pigments does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Conductive pigments, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Conductive pigments will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2532469