Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
2002-08-19
2003-06-24
Koslow, C. Melissa (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S415000, C106S419000, C106S456000, C106S031900, C106S031650
Reexamination Certificate
active
06582507
ABSTRACT:
BACKGROUND OF THE INVENTION
Laminar or plate-like pigments which impart a pearly or nacreous luster into objects on which or in which they are used are known as “effect” pigments, and have also been known as pearlescent pigments or nacreous pigments. These 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 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. 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. The result of coating a BiOCl pigment itself, however, is that some of the natural luster and brightness to be lost. It is therefore desired to improve the light stability of the bismuth oxychloride while achieving a better brightness.
It is accordingly the object of the present invention to provide an improved bismuth oxychloride effect pigment with better light stability and brightness 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 an embedded particulate of microfine titanium dioxide or zinc oxide at about the surface thereof, which can be produced by hydrolyzing a soluble bismuth salt in the presence of chloride and adding the particulate to the hydrolyzation reaction mixture before the formation of the bismuth oxychloride is complete.
DESCRIPTION OF THE INVENTION
In accordance with the present invention, the conventional production of bismuth oxychloride crystals is modified by adding a particulate to the reaction mixture before the formation of the crystals is complete or alternatively, by ending the BiOCl crystal formation, adding a dispersion of the particulate and thereafter adding an aluminum or rare earth metal salt to lock in (cement) the particulate to the crystal.
Bismuth oxychloride crystals are typically produced by combining a soluble bismuth compound with a source of chloride under acid conditions. Hydrolyzation occurs at a rate which is dependent on the concentrations of the reactants, pH and temperature. The material which is most often employed is bismuth nitrate although any soluble bismuth compound can be used. To prevent premature hydrolysis and precipitation of insoluble bismuth compounds, the bismuth salt is usually employed in the form of an aqueous acidic solution. For this purpose, the solution typically 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.
In a preferred procedure, a preformed particulate is added to the hydrolyzation reaction mixture before the formation of the desired bismuth oxychloride crystals is complete. So that the particulate is at or near the surface of the effect pigment, the bismuth oxychloride formation process is allowed to achieve about 80 to 95% completion, preferably about 85 to 90% completion, before the addition is effected. The particulate can be either microfine zinc oxide or titanium dioxide, i.e., having a particle size of less than about 500 nm. The particle size of the microfine particulate is usually at least about 5 nm, preferably at least about 10 nm and most preferably at least about 100 nm. While the particulate can be added as such, it is generally more convenient to disperse the particulate in a compatible liquid such as water or, more preferable, the liquid in which the bismuth salt was dissolved. The concentration of the particulate in the resulting slurry can be varied as desired and the viscosity is generally the controlling factor, with that which allows easy processing of the slurry being selected. Typically, the concentration of the particulate in the slurry is about 1 to 10%.
Alternatively, it is possible to finish the BiOCl crystal formation before adding the particulate but in this instance additional steps and reagents are necessary. The pH is raised to, for instance, at least about 2 to ease materials handling and then a dispersion of the particulate is added. Next, a rare earth metal salt or an aluminum salt, or a combination of salts, is introduced into the slurry and the pH is further raised to an effective deposition value, for example, to at least about 7 in the case of an aluminum salt and to at least about 10 in the case of a rare earth metal salt. The nitrate is the preferred salt. While any rare earth metal can be used, it is preferred to employ cerium.
The amount of the particulate added to the bismuth oxychloride slurry in either process is such that the particulate will generally range from about 1 to 20 weight percent, preferably about 5 to 15 weight percent, based on the weight of the bismuth salt being employed. This results in the incorporation of about 1 to 20 weight, preferably about 5 to 15 weight percent, particulate based on the total weight of the final pigment. Since the particulate is added before the formation of the BiOCl is complete or the “lock-in” procedure is used, the particulate is embedded or bound to the effect pigment at or near the BiOCl surface but does not form a smooth and continuous coating on that surface. As a result, the inherent brightness of the BiOCl effect pigment is substantially retained while at the same time, an improved light stability is achieved.
At the end of the BiOCl preparation, the resulting pigment is recovered from the slurry in which it was formed in any convenient fashion. For example, the pigment can be filtered and then washed with water until substantially free of salt. Alternatively, a settling and decanting procedure can be employed. The pigment can be dried by heating if desired.
The resulting 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 powdered product either with or without the addition of a dispersing agent. Alternatively, the filter cake can be flushed with an oil such as castor oil or mineral oil, which causes the pigment originally wet with water to become
Cao Paul B.
Venturini Michael
Dickstein Shapiro Morin & Oshinsky LLP.
Engelhard Corporation
Koslow C. Melissa
Manlove Shalie
LandOfFree
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