Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-01-04
2002-04-09
Michl, Paul R. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C106S403000, C524S431000
Reexamination Certificate
active
06369147
ABSTRACT:
The invention is directed to the field of color effect pigments. In the case of a painted surface, the effect pigment particles incorporated therein will, within the coating, align themselves parallel to the surface so that the colored paint surface, when illuminated by a fixed white light source may display different colors or will appear to have an iridescent color depending on the viewing angle. Therefore, effect pigments which are for example, incorporated in a paint coat applied to the body of an automobile, increase the visual appeal and consequently the value of the vehicle.
Effect pigments have historically been manufactured by one of two methods. In the first method, as described for example in U.S. Pat. No. 3,438,796, a goniochromatic effect pigment that displays an angle-dependent color change and consists of a central opaque aluminium film symmetrically coated with a relatively thick layer of SiO
2
, a transparent aluminium film and a thin SiO
2
film is formed by coating a substrate film alternately with SiO
2
and aluminium vapor under a high level of vacuum and scraping or otherwise removing the resulting multilayer structure from the substrate to provide pigment particles.
A refinement of the foregoing process is described, for example, in U.S. Pat. No. 5,135,812. This patent describes a process in which multiple layers are formed by vacuum deposition on either a soluble web which is then dissolved to provide a sheet of the multilayer structure which breaks into pieces upon dissolution of the web to provide pigment particles, or on a release layer provided on a flexible web. In the latter case, the multilayer structure is released and broken apart upon flexing of the web to provide particles that are then comminuted to the desired size. Both of these procedures require multiple coating and/or vacuum deposition steps which must be precisely controlled in order to provide a suitable effect pigment. Due to the number of steps involved in the process, the specialized equipment and precise process control that is required, the resulting pigments are extremely expensive.
The second of the two commonly employed methods for forming metallic effect pigments displaying goniochromatic properties is described, for example in U.S. Pat. No. 5,364,467. The process described therein involves the formation of multiple metal oxide layers directly onto metallic particle substrates by vapor phase decomposition of a corresponding volatile metal compound, i.e., carbonyls, halides and, in particular chlorides and alkoxides.
Colored pigments are also known from U.S. Pat. No. 4,328,042 that have metallic cores whose surface has been coated at least in part by iron oxide. The. metallic cores, which must be capable of producing a metallic luster, are introduced into a fluidized bed reactor and preheated to a desired reaction temperature. The preheated metallic core particles such as copper and its alloys with zinc and/or tin, or aluminium and its alloys with copper, are then contacted by an iron pentacarbonyl vapor, which oxidizes to form iron oxide and carbon dioxide. The latter two procedures have some advantages as compared with the previous ones, but it is also necessary to control all process steps very carefully, so that these pigments are quite expensive, too.
JP-10/110113 (Nippon Chemical) discloses a process for making a pigment flake characterized in that a stainless steel flake is coated with a non-specified mixture of titanium compounds comprising oxides and hydroxides, which is deposited on the stainless steel flakes in an aqueous solution containing an inorganic salt of titanium. The inorganic salt is entirely dissolved into water, if necessary with the help of an acid in small quantity (for example in the case of basic titanyl sulfate). Titanium dioxide is partially formed upon calcination, the interference color depending on the drying and calcination temperature. However, this procedure does not lead to pigments coated with pure, crystalline titanium dioxide. The results are coloristically difficult to reproduce, too, and the pigments do not possess a satisfactory sedimentation behavior for example in liquid paint compositions.
U.S. Pat. No. 5,766,334 discloses colored titanium pigment flakes having a thin (25 to 200 nm thick) superficial oxide layer formed by oxidation. EP-A-0 328 906 discloses a process for coating metal flakes, including titanium and stainless steel flakes, with a coating of titanium dioxide that has been deposited by hydrolysis of a hydrolyzable organic titanate ester under specific conditions. In order the flakes not to dissolve into a strongly acidic aqueous medium, the deposition is effected in an organic medium at a pH of 4 to 8.
The obtained coatings, however, are in both cases not satisfactory uniform in thickness, and the coloristic properties (especially the chroma) do not match high expectations.
Pearlescent silicate pigments are also known that have silicate flakes having a layer of rutile titanium dioxide or iron oxide. One such pearlescent pigment is disclosed in U.S. Pat. No. 5,753,371 wherein the coated particles are made by dispersing C glass particles in an acidic aqueous medium containing ferric chloride, titanium tetrachloride or titanyl sulfate. A layer of tin oxide may optionally be deposited as a nucleating agent prior to the titanium oxide, in order rutile to be formed upon calcination. However, the colored pearlescent pigments of U.S. Pat. No. 5,753,371 (the teachings of which are incorporated herein by reference) have coloristic properties which do still not match satisfactory the high requirements in the field.
Methods involving the deposition of a metal oxide layer via liquid phase decomposition (hydrolysis) of a corresponding metal salt (i.e., sulfate or halide) are known per se and have been used to form luster, or pearlescent pigments which have translucent, non-reflective mica cores. However, such methods, described for example in U.S. Pat. No. 3,087,827 and U.S. Pat. No. 5,733,371, have not been considered suitable for forming effect pigments with reflective metallic cores in the highly acidic (pH of less than 4), aqueous solutions required by such processes. Problems associated with the coating of reflective metal cores with a metal oxide layer by hydrolysis of the corresponding metal salt are discussed, for example, in U.S. Pat. No. 5,213,618.
Surprisingly, applicants have discovered that by selecting certain metal cores and optionally treating them in such a way that they are rendered more corrosion resistant, inexpensive effect pigments having a simple metal oxide-metal-metal oxide structure but of excellent optical properties can be obtained in a more economical way by forming a coating layer of metal oxide on the surface of the metal core or substrate by hydrolysis of the corresponding inorganic metal salt under highly acidic conditions and subsequent calcination. The metallic cores or substrates must display a reflectivity of 40% to 80% in order to produce optical variance in the resulting pigment and are suitably sufficiently resistant to aquatic corrosion to withstand immersion in highly acidic aqueous solutions (pH of 1.0 to 4.0), in the presence of the anions of metal salts, particularly chlorides. A convenient test for checking the resistance to corrosion is to immerse a polished plate of the metallic material into aqueous chlorohydric acid of pH 2 at 80° C. for 1 hour, whereby its reflectivity should not change by more than ±5%, and its thickness should not decrease by more than 1 &mgr;m, preferably not decrease by more than 0.1 &mgr;m. Suitable metals include transition metal elements and alloys thereof, preferably titanium, tantalum, zirconium, stainless steel or hastelloy (a nickel-based “super alloy”). Effect pigments based on titanium substrates are most preferred because of their surprisingly high sedimentation stability in paint media.
In view of the above-described problems and disadvantages associated with conventional processes for forming effect pigments, it is the object of the present i
Bujard Patrice
Herren Fritz
Pillonel Natacha Bonnard
Polonka Jack
Ciba Specialty Chemicals Corporation
Crichton David R.
Michl Paul R.
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