| PATENT ASSIGNEE'S COUNTRY | USA |
| UPDATE | 04.00 |
| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | 04.04.00 |
| PATENT TITLE |
Pearlescent glass pigment |
| PATENT ABSTRACT |
A pearlescent pigment comprises C glass flakes having a first layer comprising rutile titanium dioxide or iron oxide thereon and a second layer comprising hydrous oxide or hydroxide of a polyvalent cation, precipitate of said polyvalent cation, and an anionic polymeric compound. A hydrous layer of the rutile forming titanium dioxide or iron oxide is first formed on the glass flakes and the resulting coated flakes are calcined prior to the application of the second layer. |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | 02.06.97 |
| PATENT REFERENCES CITED |
Derwent Publications Ltd., XP002039404, "Flake Pigment Composition with Good Ultraviolet Radiation-Discoloration Resistance Obtained by Covering Base of Inorganic Flake Covered by Titanium Oxide or Titanium Di:oxide and Metal (HYdr)Oxide with Cerium or Antimony (Hydr)Oxide". Derwent Publications Ltd., XP002039405, "Preparation of Flake Substances Coated with Titania or Zirconia for Pearl Gloss Pigment Production by Dipping Flake in Solution Containing Hydrolysable and Poly:Condensable Organo:Metallic Compounds Containing Titanium or Zirconium". Derwent Publications Ltd., XP002039406, "Pearl Gloss Pigments Used as Fillers or Paint Pigments Consist of Flake Substrate Coated with Titania and/or Zirconium". Derwent Publications Ltd., XP002039407, "Preparation of Pearl Pigment by Coating Flaky Substrate with Titania, Zirconia and then Heat Treating". Derwent Publications Ltd., XP002039408, "Anticorrosive Coating Composition for Steel Plates Contains Glass Flakes Surface Treated with Phosphoric Acid". |
| PATENT PARENT CASE TEXT | This data is not available for free |
| PATENT CLAIMS |
What is claimed is: 1. A pearlescent pigment comprising flakes of C glass having a first coating comprising iron oxide or rutile titanium dioxide thereon, wherein the source material for said rutile titanium dioxide is selected from the group consisting of titanium tetrachloride and titanyl sulfate, and coated with a second layer comprising hydrous oxide or hydroxide of a polyvalent cation, precipitate of said polyvalent cation and an anionic polymeric substance, and water-insoluble colored pigment, the percentages of said cation, substance and pigment based on the weight of said pearlescent pigment being 0.01-20, 0.01-20, and 0.01-30, respectively. 2. The pearlescent pigment of claim 1, in which the first coating comprises rutile titanium dioxide. 3. The pearlescent pigment of claim 1, in which the first coating comprises iron oxide. 4. A method of forming a pearlescent pigment which comprises forming a first layer of hydrous rutile forming titanium dioxide or hydrous iron oxide on C glass flakes, calcining said layered flakes, forming an aqueous suspension of the calcined flakes, combining the aqueous suspension with an aqueous suspension of water-insoluble colored pigment containing an anionic polymeric substance, combining the resulting suspension with an aqueous acidic solution of a polyvalent cation which forms a hydrous oxide or hydroxide precipitate and a precipitate with said substance at a given pH and a quantity of a pH adjustment agent to provide said given pH, and recovering the resulting colored pigment. 5. A method according to claim 4, in which a first layer of hydrous rutile forming titanium dioxide is deposited. 6. A method according to claim 5, in which the first layer is formed by precipitating hydrous tin oxide on the surface of the glass flakes followed by depositing a layer of hydrous titanium dioxide thereon. 7. A method according to claim 4, in which the hydrous titanium dioxide is deposited on the glass flakes in the presence of iron and at least one member selected from the group consisting of calcium, magnesium and zinc ions. 8. A method according to claim 4, in which a first layer of hydrous iron oxide is deposited. -------------------------------------------------------------------------------- |
| PATENT DESCRIPTION |
BACKGROUND OF THE INVENTION Imparting a pearlescent luster, metallic luster and/or multi-color effects approaching iridescent can be achieved using a nacreous or pearlescent pigment which comprises a metal oxide-coated platelet. These pigments were first described in U.S. Pat. Nos. 3,087,828 and 3,087,829 and a description of their properties can be found in the Pigment Handbook, Vol. I, Second Edition, pp. 829-858, John Wiley & Sons, N.Y. 1988. The oxide coating is in the form of a thin film deposited on the surfaces of the platelet. The oxide in most wide spread use at present is titanium dioxide. The next most prevalent is iron oxide while other usable oxides include tin, chromium and zirconium oxides as well as mixtures or combinations of oxides. The coating of the metal oxide on the platelet must be smooth and uniform in order to achieve the optimum pearlescent appearance. If an irregular surface is formed, light scattering occurs, and the coated platelet will no longer function as a pearlescent pigment. The metal oxide coating must also adhere strongly to the platelet or else the coating will be separated during processing, resulting in considerable breakage and loss of luster. During the preparation of these coatings on the platelets, particles which are not attached to the platelet may form. These small particles cause light scattering and impart opacity to the pigment. If too many small particles are present, the pearlescent appearance may be reduced or lost. The addition of these metal oxide coatings to a platelet so that the luster, color and color homogeneity are maintained is a very complex process, and to date, the only platy substrate which has achieved any significant use in commerce is mica. A wide variety of other platy materials have been proposed for use as a substrate for forming these pearlescent pigments. These include non-soluble inorganic materials such as glass, enamel, china clay, porcelain, natural stones or other silicaceous substances, metal objects and surfaces of organic polymer materials such as polycarbonate. See, e.g., U.S. Pat. Nos. 3,123,485, 3,219,734, 3,616,100, 3,444,987, 4,552,593 and 4,735,869. While glass has been mentioned as a possibility on many occasions, for instance in U.S. Pat. No. 3,331,699, commercial pearlescent products are not made using glass and experience has shown that products made using glass as the platelet substrate have rather poor quality. Said U.S. Pat. No. 3,331,699 discloses that glass flakes may be coated with a translucent layer of particles of a metal oxide having a high index of refraction, such as titanium dioxide, provided there is first deposited on the glass flakes a nucleating substance which is insoluble in the acidic solution from which the translucent layer of metal oxide is deposited. The patent does not mention the necessity of a smooth transparant film, not particles, being necessary for quality interference pigments to be developed. The patent teaches that the nature of the glass is not critical, but that the presence of the nucleated surface is critical. It is further stated that there are only a small number of metal oxide compounds which are insoluble in the acidic solution and capable of forming a nucleated surface on the glass flakes; tin oxide and a fibrous boehmite form of alumina monohydrate are the only two such materials disclosed. As demonstrated in the examples below, products prepared according to the teachings of this patent are poor in quality. U.S. Pat. No. 5,436,077 teaches a glass flake substrate which has a metal covering layer on which is formed a dense protective covering layer of a metal oxide such as a titanium dioxide. In this patent, the nature of the glass is unimportant, the metallic coating provides the desired appearance and the overcoating of the metal oxide is present to protect the metallic layer from corrosive environments. It has now been determined that there is a method for preparing smooth, uniform coatings of metal oxides on glass flakes which adhere to the glass flakes to yield high quality pearlescent pigments and it is accordingly the object of the present invention to provide such a method and to provide such metal oxide coated glass flake pearlescent pigments which result from that method. It is also possible to make combination pigments containing absorption pigments which are not soluble in water and which cannot be formed in place from a water-soluble reactant or reactants. SUMMARY OF THE INVENTION The present invention relates to a pearlescent pigment and to a method for the production of such a pigment. The resulting pigment can be used in any application for which pearlescent pigments have been heretofore used such as, for example, in cosmetics, plastics, inks and coatings including solvent or waterborne automotive paint systems. DESCRIPTION OF THE INVENTION In accordance with the present invention, a pearlescent pigment is formed by establishing a hydrous film layer of titanium and/or iron oxides on glass flakes and thereafter calcining the coated flakes provided that the glass flakes employed are C glass flakes and when the hydrous layer is titanium, the procedure is a rutilizing procedure. Glass flakes are desirable in the industry because they are very resilient and can be optically attractive as well. The glass is primarily composed of SiO.sub.2 and Al.sub.2 O.sub.3 and can also include ZnO, CaO, B.sub.2 O.sub.3, Na.sub.2 O and K.sub.2 O as well as FeO and Fe.sub.2 O.sub.3. The glass flakes are made by stretching a molten glass into thin sheets, beads or glass tubes followed by crushing the glass into flakes. Large hollow spheres can be produced followed by solidification and crushing as well as a variety of other flake production methods. The flakes have a size and shape mimicking the mica platelets used in the TiO.sub.2 and Fe.sub.2 O.sub.3 -coated mica pearlescent pigments and thus have an average particle size in the range of about 1 to 250 microns and a thickness of about 0.1-10 microns. More cubic flakes having similar particle sizes and thickness of about 10-100 microns can be utilized, however, the pearlescent effect is significantly diminished due to the low aspect ratio. Glass can be classified as A glass, C glass or E glass. The A glass is a soda-lime glass and is commonly used to make windows. It contains more sodium than potassium and also contains calcium oxide. C glass, also known as chemical glass, is a form of glass which is resistant to corrosion by acid and moisture. It often contains zinc oxide as well as other oxides which makes the flakes more resistant to chemical destruction. E glass or electrical glass is, as the name implies, designed for electronic applications and although it is very stable at high temperatures, it can be susceptible to chemical attack. The following table shows the composition of several commercial samples of A, C and E glasses in weight percent. It is recognized that C glass as well as A and E glass have broad windows regarding their chemical composition and in fact A and E glass compositions can be made very similar to C glass. TABLE 1 ______________________________________ A C C E E Type Glass Glass Glass Glass Glass ______________________________________ SiO.sub.2 72.5 65-70 65% 52-56 52.5 Al.sub.2 O.sub.3 0.4 2-6 4% 12-16 14.5 CaO 9.8 4-9 14% 20-25 22.5 MgO 3.3 0-5 3% 0-5 1.2 B.sub.2 O.sub.3 0.0 2-7 5.5% 5-10 8.6 Na.sub.2 O + K.sub.2 O 5.8 9-13 8.5% <0.8 <0.5 ZnO -- 1-6 0 -- -- FeO/Fe.sub.2 O.sub.3 0.2 -- 0 -- 0.2 ______________________________________ In the practice of the present invention, the C or chemical type glass is preferred. While metal oxide coatings an A or E glass can be prepared, the resulting pigments do not have the quality of the products as C glass and hence have limited commercial value. When TiO.sub.2 coated products are prepared, anatase or rutile crystal modifications are possible. The highest quality and most stable pearlescent pigments are obtained when the TiO.sub.2 is in the rutile form. Also the glass used can influence the crystal form of the titanium dioxide coating. For instance, when common E glass is used, the resulting crystal phase is primarily anatase. In order to obtain rutile, an additive must be used which can direct the TiO.sub.2 to the rutile modification. The coating of the glass flakes with titanium dioxide or iron oxide generally follows procedures known in the art for the formation of TiO.sub.2 -coated or iron oxide-coated mica. Mica is anatase directing and, as noted earlier, most glass also appears to direct titanium dioxide coatings to the anatase crystalline form. At least some rutile formation is necessary to obtain higher quality and more stable products. In general, the procedure involves the dispersing of the glass flake particulate and combining that dispersion with a precursor which forms a hydrous titanium oxide or iron oxide film coating on the flakes. In the coating process, the glass flakes are dispersed in water, which is preferably distilled. The average particle size which is preferably used can vary from an average of about 3 microns to an average of about 150 microns and a flake thickness of 0.1-25 microns although larger flakes can also be used if so desired. The concentration of the glass flake in water can vary from about 5% to 30% although the generally preferred concentration varies between about 10% to 20%. After the glass is dispersed in the water and placed in an appropriate vessel, the appropriate titanium or iron source materials are introduced. The pH of the resulting dispersion is maintained at an appropriate level during the addition of the titanium or iron by use of a suitable base such as sodium hydroxide to cause precipitation of the hydrous titanium dioxide or hydrous iron oxide on the glass flakes. An aqueous acid such as hydrochloric acid can be used for adjusting the pH. The coated platelets can, if desired, be washed and dried before being calcined to the final pearlescent pigment. The source of the iron is preferably ferric chloride although any other iron source known in the prior art can be employed. The source of the titanium is preferably titanium tetrachloride although, similarly, other sources known in the art can be employed. If desired, layers of titanium and iron can be deposited sequentially. In the case of titanium dioxide, the modifications of the foregoing procedure to realize a rutilization procedure are known in the prior art. In one procedure, a layer of hydrous tin oxide is first precipitated on the surface of the glass flakes followed by the layer of hydrous titanium dioxide. When this layered combination is processed and calcined, the titanium dioxide is oriented in the rutile form. The procedure is described in detail in U.S. Pat. No. 4,038,099, which is incorporated herein by reference. An alternate procedure involves the deposition of the hydrous titanium dioxide on the glass flakes in the presence of iron and calcium, magnesium and/or zinc ions without the use of tin. This is described in detail in U.S. Pat. No. 5,433,779, the disclosure of which is hereby incorporated by reference. Combination pigments can be made as described in U.S. Pat. No. 4,755,229, the disclosure of which is incorporated herein by reference. Briefly, an aqueous dispersion of the colored pigment containing an anionic polymeric substance is added to a suspension of the pigment. The hydrous oxide of a polyvalent metal is then produced by the simultaneous addition of a solution of the metal salt and of a basic solution. The dispersed pigment particles and the polymer deposit with the hydrous oxide of the polyvalent metal to form a smooth, adherent, uniform coating on the pearlescent glass. In order to utilize an insoluble absorption pigment successfully in combination pigments, the insoluble pigment must be very highly dispersed. A convenient starting point is the dry pigment or preferably an aqueous presscake of the pigment. 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 pigment dispersion is combined with a suspension of coated glass pigment. 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 pigment is deposited on the platelets to form a smooth, uniform, colored coating. The suspension can then be filtered, and the filter cake washed with water and dried, for example, at 120.degree. C., to produce an easily dispersible powder of the combination pigment. Absorption pigments 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 pigments in the following groups: azo compounds, anthraquinones, perinones, perylenes, quinacridones, thioindigos, dioxazines, and phthalocyanines and their metal complexes. The pigments, depending on their color intensity, are used in a concentration range of about 0.01% to about 30% based on the weight of pigment, 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 pigment. 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 pigment. 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 pigment platelets a complex of metal hydroxide or hydrous oxide and polymer which carries the particles of the absorption pigment with it, to produce a combination pigment with a smooth, adherent colored film on the platelets. After the deposition, the film can be fixed by washing and drying the combination pigment. Colors may be adjusted if desired by mixing combination pigments. In general, it is preferred to mix pigments of the same or similar reflection color, since reflection colors mix additively and color intensity is reduced when very different reflection colors are mixed. The absorption pigment components mix subtractively, and the usual pigment blending procedures are followed. In order to further illustrate the invention, various non-limiting examples are set forth below. In these, as well as throughout the balance of this specification and claims, all parts and percentages are by weight and all temperatures are in degrees centigrade unless otherwise indicated. |
| PATENT EXAMPLES | This data is not available for free |
| PATENT PHOTOCOPY | Available on request |
|
Want more information ? Interested in the hidden information ? Click here and do your request. |