Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
2002-05-14
2003-06-17
Bell, Mark L. (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S415000, C106S456000, C106S479000
Reexamination Certificate
active
06579357
ABSTRACT:
BACKGROUND OF THE INVENTION
Effect pigments, which are also known as pearlescent pigments or nacreous pigments, are well known. These are laminar or plate-like pigments which impart a pearly or nacreous luster into objects on which or in which they are used. The known effect pigments include naturally occurring substances such as pearlescence, a mixture of guanine and hypoxanthine which is obtained from the scales of fish, as well as various synthetic materials. The effect pigments which are most often encountered commercially are titanium dioxide-coated mica and iron oxide-coated mica. Other synthetic effect pigments which have been developed for both cosmetic and industrial use include materials such as bismuth oxychloride and lead carbonate.
Bismuth oxychloride has been used as an effect pigment in a number of fields. It is used, for instance, as a pigment in cosmetics, such as nail enamels and lipsticks, and it is also used to pigment plastics and paints. The coating of a bismuth oxychloride-coated mica pigment with hydrous titanium hydroxide is described in U.S. Pat. No. 3,980,491 and the coating of a metal oxide-coated bismuth oxychloride with zinc oxide is described in U.S. Pat. No. 5,344,488. Coprecipitation of bismuth oxychloride and titanium dioxide on a mica substrate is described in U.S. Pat. No. 3,822,141. U.S. Pat. No. 2,995,459 discloses combining a synthetic pearlescent substrate, including bismuth oxychloride with insoluble metallic compound coloring agents such as the sulfides, molybdates, tungstates, xanthates and dithiazones of Cd, Mn, Co, Fe and Sb but cautions that formation of a randomly deposited unoriented coating destroys the luster of the pigment. U.S. Pat. No. 5,958,125 discloses a pigment based on a substrate, which can be bismuth oxychloride, having at least one layer packet of a colorless coating having a refractive index of 1.8 or less and a reflecting absorbing coating, of which iron oxides are examples. The iron oxide coated product, however, cannot be dried without causing clumping of the iron oxide in the coating. This is not a problem when the pigment is employed in a paste but is, of course, significant in other uses.
In order to extend the range of applications, bismuth oxychloride pigments have been coated with such materials as 2-hydroxy benzophenones and rare earth metals in order to impart ultraviolet stability or weather fastness properties to the effect pigment. See, U.S. Pat. No. 5,149,369. The result of coating a BiOCl pigment itself, however, is that some of the natural luster and brightness is desired to improve the light stability of the bismuth oxychloride while achieving a better brightness and dispersability of the product.
It is accordingly the object of the present invention to provide an improved bismuth oxychloride effect pigment with a better appearance (brightness) and greater dispersability and to provide a method for producing such a pigment.
SUMMARY OF THE INVENTION
The present invention relates to an improved bismuth oxychloride effect pigment and a process for its production. More particularly, the invention relates to an improved bismuth oxychloride effect pigment having a discontinuous surface coating of hydrous iron oxide which can be produced by hydrolyzing a soluble bismuth salt in the presence of chloride followed by coating the resulting crystals with hydrous iron oxide. The iron coating generates a decorative effect with colors ranging from gold to dark brown (champagne) depending on the amount of iron, while imparting greatly improved ultraviolet light stability, preventing photo darkening.
DESCRIPTION OF THE INVENTION
In accordance with the present invention, bismuth oxychloride crystals are grown in any conventional manner and are then discontinuously coated with hydrous iron oxide.
Bismuth oxychloride crystals are typically produced by combining a soluble bismuth compound with a source of chloride under acid conditions. While any soluble bismuth compound can be used, the material which is most often employed is bismuth nitrate. The bismuth salt is usually employed in the form of an aqueous acidic solution to prevent premature hydrolysis and precipitation of insoluble bismuth compounds. For this purpose, the solution usually contains a compatible mineral or other strong acid. Hydrochloric acid and a mixture of hydrochloric and nitric acids are particularly convenient since they serve as a source of the chloride ions which are used to form the bismuth oxychloride. The bismuth compound is hydrolyzed by maintaining the acidity within desired limits, usually about pH 1, by adding a suitable base to neutralize acid which forms during the hydrolysis reaction. The base most often used is an alkali metal hydroxide, particularly sodium hydroxide, but other soluble sources of hydroxyl ions, such as a strongly basic amine or a base precursor such as urea, can also be used.
The preparation of the bismuth oxychloride crystals is generally effected at a temperature between about 50° C. and 100° C. and more preferably about 60-80° C. Usually the soluble bismuth salt solution and the base are pumped into an aqueous acidic reservoir. Any desired bismuth oxychloride crystal size can be realized by regulating the amount of the bismuth solution which is used.
To the resulting bismuth oxychloride crystals is added a hydrolyzable source of iron. Preferably, the iron is provided in the form of an aqueous solution of a water soluble iron salt such as ferric chloride and ferric sulphate. The pH of the resulting slurry is then adjusted such that the iron salt undergoes hydrolysis and becomes a coating on the surface of the bismuth oxychloride crystals. Any suitable base can be used to adjust the pH and as in the case of the hydrolysis of the bismuth compounds, an alkali metal hydroxide, particularly sodium hydroxide, can be used. The hydrous iron oxide is formed by changing the pH of the bismuth oxychloride environment so that it is in a range of about 2 to 4,and more preferably about 2.75-3.25. The hydrolysis of the iron can be effected at a temperature between ambient and about 100° C. and preferably at about 60 to 80° C.
The amount of the iron solution added to the bismuth oxychloride slurry depends on the desired color of the effect pigment. As the amount of the iron increases, the absorption color changes. In general, the amount of the iron salt added will range from about 1 to 70 weight percent depending on the desired color, preferably about 10 to 40 weight percent, based on the weight of the bismuth oxychloride crystals in the slurry. This results in the formation of a hydrous iron oxide coating on the bismuth oxychloride crystals in which the coating amounts to about 0.1 to 70 weight, preferably about 10 to 40 weight percent, of the total weight of the pigment. As a result of depositing the hydrous iron oxide before the bismuth oxychloride is isolated from the reaction mixture, a continuous coating is not formed. Therefore, the coating is not smooth and continuous but rather the hydrolyzed iron concentrates in a plurality of small clumps and thereby forms a discontinuous coating on the BiOCl. That, in turn, results in the inherent brightness of the BiOCl effect pigment continuing to be visible and being substantially retained. In addition, the discontinuous coating allows the final product to be dried without the iron oxide clumping.
At the end of the hydrous iron oxide precipitation, the resulting pigment is recovered from the solution in which it was formed in any convenient fashion. For example, the pigment can be filtered and then is preferably washed with water until substantially free of salt. Alternatively, a settling and decanting procedure can be employed. The pigment can be dried by heating or air dried, if desired, but temperatures which convert the hydrous iron oxide to iron oxide should be avoided.
The resulting hydrous iron oxide coated BiOCl effect pigment is thereafter processed in the conventional manner into various types of finished products. For example, the filter cake can be dried to produce a pow
Bell Mark L.
Dickstein , Shapiro, Morin & Oshinsky, LLP
Engelhard Corporation
Manlove Shalie
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