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This invention deals with colore d nacreous pigmen ts and with processes for producing these pigmen ts.

Nacreous pigmen ts produce pearl-like, metallic, and iridescent effects. A widely used type comprises muscovite mica platelets coated with a metallic oxide, such as titanium dioxide. A relatively thin titanium dioxide coating produces a pearl-like or silvery luster. Mica platelets with thicker coatings produce color< /span>, even though the components are colorless, through the phenomenon of light interference; they are known as interference pigmen ts. The color< /span>, called the reflection color< /span>, is seen most effectively by specular or mirror-like reflection, where the angle of reflection equals the angle of incidence. The reflection color< /span> is a function of optical thickness, i.e. the geometrical thickness times the refractive index, of the coating. Optical thickness of about 80 nm to about 140 nm produce reflections which may be called white, silvery or pearly; optical thickness of about 190 nm or more produce colore d reflections.

Combination pigmen ts are more complex. The oxide-coated mica pigmen t is further coated with an absorption pigmen t or dye, so-called because it absorbs some portion of the visible spectrum. If the absorption colora nt has the same hue as the reflection color< /span> of the oxide-mica pigmen t, that color< /span> is intensified and is seen over a wide range of angles; if it has a different hue, the reflection color< /span> or a color< /span> close to it is seen at the specular angle, whereas the hue of the absorption pigmen t is seen at other angles. In some cases, transition colors may be seen between the extremes. Thus a single pigmen t has more than one color< /span>. The absorption colora nt coat should be uniform and should adhere firmly to the oxide-coated mica particles.

In known combination pigmen ts, the desired results are achieved by depositing the colora nt or a precursor on the pigmen t platelets from aqueous solution. For example, U.S. Pat. No. 4,309,480 teaches that iron blue (ferric ferrocyanide) may be precipitated onto TiO 2 -coated mica by the reaction of ferric chloride and potassium ferrocyanide in aqueous solution. Aluminum hydroxide may be precipitated after the iron blue or simultaneously with it, but it is not required for the formation of the iron blue coating. U.S. Pat. No. 3,951,679 shows that an Fe(II) phosphate layer may be precipitated onto mica pigmen ts from aqueous solution and then converted in place to ferrous ferrocyanide by reaction with ferrocyanide solution, followed by oxidation in place to ferric ferrocyanide. U.S. Pat. No. 4,084,983 describes the formation of colore d lakes on mica pigmen ts by first depositing aluminum hydroxide on the surface from soluble reactants and then reacting with a dye in solution

Many colore d pigmen ts of very desirable properties cannot be formed from a water-soluble reactant or reactants. In the present invention, such insoluble pigmen t particles are dispersed in water and then deposited on the surface of the mica platelets to form continuous, adherent, and smooth colore d coatings, creating a new class of combination pigmen ts.

It is an object of the present invention to make combination pigmen ts containing absorption pigmen ts which are not soluble in water and which cannot be formed in place from a water-soluble reactant or reactants. Examples are pigmen ts like the phthalocyanines, quinacridones, perylenes, dioxazines, and carbon black. Although insoluble in water, these pigmen ts can be dispersed in water. They have high color< /span> intensity, lightfastness and bleed resistance, properties which make the resulting combination pigmen ts suitable for automotive finishes as well as for general use in paints and in plastics incorporation. They are also useful in cosmetics when cosmetically acceptable components are employed.

SUMMARY OF THE INVENTION


In the present invention, an aqueous dispersion of the colore d pigmen t containing an anionic polymeric substance, such as albumin or xanthan gum, is added to a suspension of the mica or oxide-coated mica pigmen t. The hydrous oxide of a polyvalent metal, for example chromium(III) or aluminum(III), is then produced by the simultaneous addition of a solution of the metal salt and of a basic solution. The dispersed pigmen t particles and the polymer deposit with the hydrous oxide of the polyvalent metal to form a smooth, adherent, uniform coating on the mica platelets. While not wishing to be limited to theory, it is likely that the polymer reacts with the polyvalent metal to form a complex hydrous oxide.

The resulting combination pigmen ts exhibit brilliant color< /span> and color< /span> play, the specific colors depending on the reflection color< /span> of the original oxide-mica pigmen t and the color< /span> of the deposited pigmen t.

DETAILED DISCUSSION


Coated mica pigmen ts are now well known and widely used to produce pearlescent, metallic, and iridescent effects. Colorless oxides, such as TiO 2 and ZrO 2 , are described as coatings for mica in U.S. Pat. No. 3,087,828. Colore d oxides, such as Fe 2 O 3 , Cr 2 O 3 , etc., appear in U.S. Pat. No. 3,087,829. Interference pigmen ts of a colorless oxide coated on mica are of particular interest, because the color< /span> is derived entirely from the interference effect. They make possible combination pigmen ts with the widest range of colors : any desired reflection color< /span> is obtainable by controlling the thickness of the oxide coating, and absorption pigmen ts of any desired color< /span> are available for overcoating. For example, a blue-reflecting TiO 2 -coated mica overcoated with a red absorption colora nt appears blue at the specular angle and primarily red at other angles. If the oxide coating consists of or includes a colore d oxide, the pigmen t itself already has a reflection color< /span> and an absorption color< /span>; the latter modifies the color< /span> of the absorption pigmen t overcoating.

In some cases, the absorption colora nt can shift< /span> the hue of the reflection color< /span> to some extent. This factor is taken into account in deciding on the thickness of the oxide coating to be deposited on the mica.

In order to utilize an insoluble absorption pigmen t successfully in combination pigmen ts, the insoluble pigmen t must be very highly dispersed. A convenient starting point is the dry pigmen t or preferably an aqueous presscake of the pigmen t. After dilution with water or other liquid, such as alcohol, dispersion is achieved by any one of the usual techniques, such as milling, high shear mixing, or application of ultrasonic energy. The desired degree of dispersion is similar to that conventionally used in paint and coating formulations. It is preferred to add the anionic polymer prior to or during the dispersion step in order to assist the dispersion process.

The polymer-absorption pigmen t dispersion is combined with a suspension of mica or oxide-coated mica. The pH of the resulting suspension should be in the range suitable for precipitation of the desired polyvalent cation hydroxide or hydrous oxide, generally between about pH 1 and 11, and most frequently between about pH 2 and 8. A solution of soluble salt of the polyvalent cation is then added to the suspension simultaneously with a quantity of a basic material soluble in the solution sufficient to maintain the pH in the desired precipitation range. The absorption pigmen t is deposited on the platelets to form a smooth, uniform, colore d coating. The suspension can then be filtered, and the filter cake washed with water and dried, for example, at 120° C. to produce an easily dispersible powder of the combination pigmen t.

The anionic polymer is a necessary component in this procedure. Without it, the absorption pigmen t particles are likely to agglomerate during the polyvalent cation addition and do not deposit on the substrate.

The procedure is effective on mica as well as oxide-coated mica and hydeous oxide-coated mica. The oxide coatings may be of TiO 2 , ZrO 2 , SnO 2 , ZnO, Fe 2 O 3 , Cr 2 O 3 , V 2 O 5 , and the hydrous forms thereof. The oxide may be present in various crystalline forms, for example, TiO 2 can be anatase or rutile. Combinations of oxides of two or more metals may be used. The colorless oxides allow the greatest freedom in choice of absorption colora nt; the color< /span> of the colore d oxides influences the choice of absorption colora nt because the final absorption color< /span> is determined by the mixture of the two colors .

The oxide coating typically has an optical thickness from about 80 to about 600 nm. The mica platelets are from about 3 to about 100 μm in their longest direction, and from about 0.1 to 1 μm in thickness.

Suitable types of mica for the micaceous pigmen ts of the invention are muscovite, phlogopite, biotite, and synthetic micas. Muscovite is the preferred natural mica because its own light color< /span> does not adversely affect the color< /span> of the absorption pigmen t.

Absorption pigmen ts which are water insoluble, transparent (i.e. substantially non-light scattering) and which cannot be formed in situ from a water soluble reactant(s) but which may be highly dispersed in water or water-alcohol containing anionic polymer are suitable for the invention. These include, for example, carbon black and organic pigmen ts in the following groups: azo compounds, anthraquinones, perinones, perylenes, quinacridones, thioindigos, dioxazines, and phthalocyanines and their metal complexes. The pigmen ts, depending on their color< /span> intensity, are used in a concentration range of about 0.01% to about 30% based on the weight of mica pigmen t, preferably 0.1% to 10%.

The useful polymers are those which are capable of precipitating with polyvalent cations at the appropriate pH values. Thus, the polymers are usually anionic, or, like proteins, have both anionic and cationic groups. Useful polymers include albumin, gelatin, polyacrylamides, polyacrylic acids, polystyrene sulfonates, polyvinyl phosphonates, sodium carboxymethyl cellulose and polysaccharides such as xanthan gum, alginates, and carageenin. The polymer content is from about 0.01% to about 20%, preferably from 0.05 to 10%, based on the weight of the mica pigmen t.

Any polyvalent cation which will form a precipitate with the polymer under given pH conditions can be used. Such polyvalent cations are employed in the form of a solution of a soluble salt. Thus, the cation can be, for example, one or more of Al(III), Cr(III), Zn(II), Mg(II), Ti(IV), Zr(IV), Fe(II), Fe(III), and Sn(IV). Suitable anions include chloride, nitrate, sulfate, and the like. The quantity of polyvalent metal ion is from about 0.01% to about 20%, preferably about 0.05% to about 10%, of the weight of the mica pigmen t.

The preferred pH range for deposition depends on the particular cation being employed. For Al and Cr(III), it is about 4.0 to 8.0. For Zr(IV), it is about 1.0 to 4.0. The metal salt solution is usually acidic, and the pH of the suspension is maintained at the desired range by addition of a soluble base, such as sodium hydroxide, potassium hydroxide, or ammonia solution. Where the desired pH of precipitation is lower than that of the salt solution, a soluble acid, such as HCl, is added as required.

The effect in each case is to deposit on the mica pigmen t platelets a complex of metal hydroxide or hydrous oxide and polymer which carries the particles of the absorption pigmen t with it, to produce a combination pigmen t with a smooth, adherent colore d film on the platelets. After the deposition, the film can be fixed by washing and drying the combination pigmen t.

The use of chromium as the polyvalent cation for the coating of a rutile-coated mica is of particular interest, inasmuch as chromium hydroxide imparts high resistance to weatherability stress to such pigmen ts, as disclosed in U.S. Pat. No. 4,134,776. The products are suitable for exterior use in such applications as automotive finishes, roof tiles, outdoor furniture, and the like.

The combination pigmen ts of this invention have advantages over multicolor effects obtained by incorporating the mica pigmen t and absorption pigmen t separately in a paint or lacquer vehicle. No dispersion step is required for the absorption pigmen t, since it is already dispersed for maximum effectiveness on the mica pigmen t surface. The oil absorption requirement of the combination pigmen t is less than that of the sum of the separate pigmen ts. The tendency of absorption pigmen t particles to flocculate is eliminated or greatly reduced when the particles are bound to the micaceous platelets. Also, the paint formulator has the convenience of working with fewer components because a two- color< /span> effect is achieved by a single pigmen t.

Colors may be adjusted if desired by mixing combination pigmen ts. In general, it is preferred to mix pigmen ts of the same or similar reflection color< /span>, since reflection colors mix additively and color< /span> intensity is reduced when very different reflection colors are mixed. The absorption pigmen t components mix subtractively, and the usual pigmen t blending procedures are followed.

The new combination pigmen ts may be used in all the usual applications for nacreous pigmen ts: in paints and other coatings, incorporated in plastics, and in cosmetics when the components are acceptable for this use. Furthermore, the specific colors of the combination pigmen t may be modified, if desired, by the addition of other absorption colora nts to the formulation in the conventional way.

The preparation of the combination pigmen ts are best illustrated by the following non-limiting examples:

EXAMPLE 1

Quinacridone red on blue-reflecting anatase-coated mica


An aqueous presscake of quinacridone red (Sunfast Red 19, Sun Chemical Co., 23.7% pigmen t) was diluted to 0.50% pigmen t with water. To 250 g of this suspension was added 0.1 g xanthan gum (Kelzan, a microbiolal polysaccharide containing glucuronic acid, Kelco Division). Ultrasonic energy was applied by means of a Sonifier® Model 350 (Branson Sonic Power Co.) for 30 minutes to disperse the pigmen t.

The mica containing pigmen t substrate was 50 g of blue-reflecting TiO 2 -coated muscovite mica (most platelets about 5-50 μm long, average thickness about 0.5 μm, 46% TiO 2 ), suspended by stirring in 400 g of water. The pH value of the suspension was 9.0, and was adjusted to 6.0 with 0.1 N HCl. This suspension was combined with quinacridone red dispersion; there was no significant pH change. A solution of 2.64 g CrCl 3 .6H 2 O in 165 g water was added at a uniform rate in 100 minutes while maintaining the pH at 6.0 with 3.5% (by weight) NaOH.

Examination of the resulting suspension by optical microscope at 1000× magnification showed that all the red pigmen t was deposited on the micaceous platelets to form a smooth, uniform red coating. The suspension was filtered, and the filter cake was washed with water. The filtrate and washings were clear and colorless. The filter cake was dried at 120° C. for 1 hour.

Incorporated at 3% by weight in a paint vehicle of the following composition: