Improvements in pigment compositions

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PATENTS AND REGISTRATION OFFICE

PUBLISHING WRITING No. 320 135 int ci C 09 c 3/00 ki.22 f 10

Patent Application. No 7175/62 Received on 27 VI 1962

Validity Day, 27 VI 1962

Atis. generally available on 1 VII 1968

Ans. laid out and the pamphlet published on 2 II 1970

Priority requested from 28 VI 1961 (OSA, 120 157, 120 ΐ # 7)

Ε. I. DO PONT DE NEMOURS AND CO., WIIMINGTON, DEL., USA Inventors HR Lin-ton Ombudsman N Larfeldt

Pigment composition and process for making the same

The present invention relates to novel pigment compositions. A class of pigments which have previously been widely used can be denoted by the general term flake pigment. with the surface of the paint or other film.

Painted in water, white mica in small size (200 - 325 mesh) has been widely used for this purpose.

Other types of flake pigments include metal flakes, especially &lt;1 aluminum in various particle sizes, which flakes have been used for both reinforcement and to provide substantial opacity and glossy surfaces for such flakes which give a film with the same appearance as a metal surface.

Metal flake pigments, such as aluminum, have also been found extensively covered ¹ use due to their decorative effect, especially in admixture with other pigments, thus obtaining the well-known metallized appearance of many moving surfaces. Despite their suitable appearance, such metallized surfaces have some well-known imperfections, including a tendency to water stains. It is also common to find that a mixture of aluminum flakes and colored pigments is less light-resistant than just the colored one. i ', in the pigment.¹

A third and more specialized use of certain flake pigments is in: providing surfaces with a pearl-like or pearl-like effect 5 mimicking the appearance of pearls with its three-dimensional gloss effect in the depth of the film. Pigments of this action are non-opaque with a high refractive index and vary in nature from an extract of fish scales, essentially the organic compound guanine, to flake-like crystals of certain inorganic salts, especially basic lead carbonate and acidic lead phosphate. Despite their valuable decorative properties, these products have well-known imperfections, such as:

1st They generally cannot be handled in dry form but must be stored and sold as dispersions in selected carriers in which they will be used.

j 2. Their light fastness does not match the requirement in many outdoor applications.

!

3rd They are in themselves very precious to produce.

4th The presence of lead compounds is unsuitable in many potential applications.

The present invention relates to a new group of pearl-like flake pigments, which can be sold in dry, healed dispersible form and which have excellent light fastness and are mostly non-toxic and of relatively low cost. They have the ability to be assembled so that highly desirable pearl-like effects are achieved and, moreover, within the large group there are many products with distinctive color in addition to the pearl-like property epitome, the color at least in part resulting from optical interference phenomena. In addition, these products can also be assembled to mimic a metallized appearance, which is completely free of water stains, which are so distinctive on surfaces based on aluminum flakes. Finally, since they are flake-like and chemically stable, they have the additional ability to serve as reinforcing pigments.

All pigments, which exhibit pearl-like effects, when dispersed in carriers, have some common optical and physical characteristics which distinguish them from the usual colored pigments and the trade white pigments. In contrast to irregularly shaped pigment particles which behave very similarly to small spheres, pearl-like pigments are non-opaque, flake-like products in which the optical units are extremely thin flakes of greater diameter at least about 5-10 microns and the thickness in the range of about 0 , 1-3 microns. Such optical devices reduce light scatter and lead to direct reflection or sparkle.

All pearl-like pigments must be translucent or transparent and / or must exhibit a significant difference in refractive index from the medium in which they are dispersed. Thus, common carriers for coating compositions, plastics and the like generally have a refractive index in the range of about 1.5 to 1.6. Those pigments, previously known as pearl-like pigments, generally have a refractive index in the range of about 1.8 - 2.6. Most known pearl-like pigments are thin flakes of a certain chemical compound. These thin flakes exhibit, in the presence of a low refractive index carrier, the optical appearance of thin films, including light interference and a resulting film interference color property. Known flakes, however, exhibit more or less arbitrary thickness and the average effect is a mixture of colors, giving a pearl-like or pearl-like appearance which is almost free of discernible color.

The optical principles that explain interference colors are well known and discussed in many physical optics manuals, such as Robert W. Wood - Physical Optics - Edition 3, New York, 1936, p. 198

The present invention relates to a pigment composition consisting essentially of luminous, mica-like flakes having on the surface a thin, adhesive, luminous layer of any of the following metal oxides: aqueous titanium dioxide particles, colorless titanium dioxide particles, aqueous zirconia particles, colorless zirconia particles, iron (III) oxide, chromium (III) dioxide, vanadium (V) oxide, aqueous iron (III) oxide and aqueous chromium (III) oxide thickness of at least 20 millimicrons.

The new pearl-like flake pigments of the invention consist of two parts, (1) a non-opaque flake substrate and (2) a thin adhesive, luminous layer of either (a) titanium or zirconia with an optional second oxide as a separate layer; or in admixture with the titanium or zirconium oxide or (b) one of the colored metal oxides iron (III) oxide, chromium (III) oxide_l vanadium (V) oxide and aqueous oxides of iron (III) and chromium (III).

In a suitable embodiment of the present invention, the non-opaque flake substrate is a flake-like, mica-containing mineral, usually muscovite mica, in the selected particle size range. Such flake substrates useful in the present invention are particles having two dimensions (length and width) of similar size and typically much larger than the third dimension. In particular, light flakes according to the invention are in particular at least about 5-10 in

microns in the main dimension and about 0.05 - 1.0 microns in thickness. For most pigment purposes, the upper limit of the main dimension is from 50 to 100 microns. However, for special purposes, such as in plastic articles of considerable thickness, linoleum and the like, larger flakes up to as much as 1 mm in length can be used for special decorative effects. The lower limit in the thickness of the mica flake is largely determined by the physical strength of the flake and can be as small as 0.05 microns or even less, while an upper limit of about 3.0 microns. accompanied by a correspondingly greater length and width, is determined by the effect on the surfaces of the coating composition. Such flakes must also be substantially planar with a relatively even and light reflecting surface and must be insoluble in either water or organic solvents and inert to them.

A satisfactory mica quality is a water-milled white shimmer, often used as an active filler pigment in color, in which all particles pass through a 200 mesh screen and $ 90 through a 325 mesh screen. However, for special purposes it is very possible to use flakes that are in the interval; 140 - 200 mesh on the one hand as well as materials that are significantly finer and approach the 400 mesh size or even finer.

Another measure of particle size, which is in many ways more easily correlated with the application of subsequent metal oxide films to the surface, is the specific surface area, measured by gas adsorption using the well-known Β.Έ.T. method described by Emmet in Advances in

Colloid Science vol. 1, New York, Interscience Publishers, Inc., 1942, p. 1-35 · This feature has been found to vary considerably from batch to batch of mica with nominally equal size. Mica having a surface o of about 3 m / g and having a fairly uniform particle size is a particularly suitable shape. However, products with acceptable properties can be obtained from mica samples with widely different surfaces, provided that appropriate corrections are made to the amount of metal oxide applied to form the transparent layers thereon, so that the use of metal oxide per unit surface is appropriately regulated. Some arbitrary limits on the surface cannot be determined, but an interval of about 2 to about 7 m / g will comprise products which are most suitable. In addition to the preferred muscovite or white mica, other forms of mica may be used as substrates according to the invention, such as biotite, phlogopith, the related vermiculite and various synthetic mica species. For the preparation of these products in a suitable batch size range, it is convenient that they are also ground in water. The introduction of agents to facilitate cleavage or the introduction of other inert coatings which do not substantially alter the refractive index of the glitter or its susceptibility to the subsequently applied luminous oxide layer are considered to be within the scope of the invention. The natural color of some of these mica species affect the color of the final products, but the interfering colors of the deposited layers still exist.

Suitable materials for the thin, translucent layer of metal oxide deposited on the mica substrate are iron (III) oxide, chromium (III) oxide, vanadium (V) oxide, aqueous oxides of iron (III) and chromium (III), and one oxide. of tetravalent titanium, such as TiCl 3, wherein the particles of these oxides are less than 0.1 microns in diameter.

The metal oxide layers in aqueous form (wherein the aqueous vanadium oxide is a vanadium (IV) oxide) are conveniently deposited on mica substrates by suspending mica in acidic solutions of suitable metal salts. thereby providing a carefully controlled hydrolysis at such a rate that the mica flakes are capable of acting as cores for the formation of aqueous oxide layers on their surfaces. The exact physical conditions for achieving this slow formation of aqueous oxide vary somewhat with the metal used.

When the deposited metal oxide is an oxide of tetravalent titanium such as

Ten₂, deposited | the aqueous oxide layer is conveniently on a mica substrate by suspending the mica in a dilute, highly acidic solution of titanyl sulfate at ambient temperature and thereafter hydrolyzing the titanium sulfate solution by rapid heating to ca.

90 - 100 ° C, at which temperature the solution is maintained for about 2-3 hours, so that the aqueous titanium dioxide, when formed, is continuously deposited on the mica with a minimum of formation of free aqueous titanium dioxide. Alternatively, the mica may be suspended in hot water, to which is then rapidly added a highly acidic, concentrated titanyl sulfate solution, after which hydrolysis and aqueous titanium dioxide deposition on the mica is accomplished by continuing heating during boiling until the hydrolysis is complete. The choice between these methods is a suitable choice.

After isolating the pigments obtained by filtration and drying, pearl-like powders exhibiting glossy interference colors are obtained when dispersed in a carrier, the predominant color (at least in part) depending on the thickness of the aqueous oxide film.

The color of the products thus obtained is fairly indeterminate and is most easily observed when a film containing these new pearl-like pigments is observed over a dark background. In addition to the predominant interference color, substantially all of these products exhibit a shiny rainbow shimmer or a multi-colored glitter when viewed at mirror angle under shining lighting, such as in sunshine. This combination of rainbow shimmer on a background of a predominantly color is an outstanding feature of the new products.

The new products containing aqueous TiCl3 on mica, as prepared directly by the hydrolysis of a titanyl sulfate solution in the presence of mica, are very beautiful in color effects and useful for some purposes, where they are not generally exposed to light, fully photosensitive, whereby shown marked changes in the pigmented compositions containing them upon exposure to light. Accordingly, they require stabilization in this property for their most effective applications. This photosensitivity is considered to be partly due to either of two reasons. On the one hand, dry, aqueous TiC 3 constantly contains a significant amount of acidic impurities which cannot be removed by conventional pigment isolation techniques. Partial stabilization of the sensitivity due to this cause can be achieved by deposition of certain other metal oxides, especially aqueous alumina or aqueous chromium oxide on the layer prior to final drying. However, more effective stabilization is achieved by calcination at temperatures in the range 700-1000 ° C, preferably 900^_1000 ° C. Products obtained by calcining in these temperature ranges retain their shiny interference colors to a large extent, although the predominant colors shift slightly in the direction that shows a reduction in the thickness of the oxide layer, as might be expected by the expulsion of certain impurities, including water and residual acid.

It is well known that certain impurities have a profound effect on the sensitivity of light to titanium dioxide. This effect is also found in TiO₂pigments according to the invention. For example, very small amounts of iron, which can be introduced by the use of impure raw materials or by migration from mica during calcination, have been found to cause, for example, the sensitivity to light. On the other hand, certain impurities can be arbitrarily introduced by the appropriate selection of raw materials or the addition of suitable: salts to the titanyl sulfate solution to provide remarkable improvements in reduced photo sensitivity. Compounds of antimony, niobium, chromium, tungsten, molybdenum and even iron, used in substantial quantities, serve in this way. A particularly valuable method is to add small amounts of an antimony compound, e.g. antimony oxide (in the range of 0.5 to 7&gt;, preferably about 2%, based on the titanium present) prior to calcination. In any case, small amounts of a second metal oxide, not exceeding about 20% by weight of the titanium oxide, may be contained in ten. tan oxide layer either as a contaminant or by arbitrary simultaneous precipitation.

An alternative method of depositing the film of titanium dioxide involves exposing hot (+ 600 ° C) mica flakes to the vapor of an organic titanate ester, such as tetraisopropyl titanate, in the absence of air or water vapor, and preferably in vacuum »Other water-soluble salts of titanium may also be used. hydrolysis. In particular, titanium oxychloride, as well as certain water-soluble titanium esters, on the other hand, such as titanium acetylacetonate and triethanolamine titaniumate, may be used.

In addition, a zirconium dioxide coating can be used in place of the titanium dioxide coating. It can be applied in a similar manner and in similar amounts by hydrolysis of a solution of a suitable zirconium salt (e.g., zirconium oxychloride or zirconium sulfate) in the presence of mica. It is a peculiarity of aqueous zirconia that it has a significantly lower refractive index than aqueous titanium dioxide, so that products containing single layers of aqueous zirconia are significantly less pearl-like than products containing titanium oxide. When calcined, however, a distinct pearl-like appearance is elicited.

When the layer is iron oxide, it is convenient that a substantial amount of acetate ion is added to a solution of an iron (III) salt and that hydrolysis is effected by gentle heating of the resulting solutions.

Other buffer salts, on the other hand, are suitable in the preparation of chromium and vanadium oxides, which can be done without heating by the addition of a solution of a suitable buffer salt at room temperature, the buffer agent being selected to provide the appropriate pH for the formation of aqueous oxide with relatively slow speed. One. process can also be used in depositing aqueous iron oxide on mica. A suitable agent for use in this case is borax (Na₂B2jO +. 10H₂0). It is convenient to add the borax in small portions so that the pH is maintained at a desirable range, as further shown in the Examples.

The metal salts selected for the preparation of the chromium, vanadium and iron oxide products of the invention are not critical to the anion present, the choice being generally controlled by availability. When precipitating an iron (III) oxide, it is customary to work with FeCl-j as an available crystalline material. However, it is equally possible to use an iron (III) sulfate solution, which can be obtained, for example, by oxidation of a solution of iron (II) sulfate (iron vitriol). Other water-soluble iron (III) salts can also be used to the extent they are available.

In the selection of chromium salt, it is customary to use a chromium sulphate solution obtained by reducing readily available sodium or potassium dichromate solutions. Another commonly available salt is chromium chloride.

A commonly available vanadium salt is vanadyl sulfate (VOSÖÖ), a quaternary vanadium derivative. Simple vanadium salts are generally decomposed into vanadyl derivatives in water, so the latter must be used.

Stable aqueous solutions of these chromium, vanadium and iron salts

You are strongly acidic and aqueous oxides precipitate when the acidity is neutralized. For the purposes of the present invention, wherein the oxide is applied as a layer of mica flakes, it is necessary that the precipitation of aqueous oxide be relatively slow. This is conveniently accomplished by the introduction of an oxygen-absorbing buffer salt, wherein sodium acetate and sodium tetraprate are suitable, although any other buffer salt which operates at a suitable pH range, e.g. about

4-7.

The concentrations of metal salt solutions can vary within a wide range, e.g. from as much as about 20% down to about 2 preferably in the range. about 2 - 10 J5.

The amount of saline in relation to mica is of importance only as a way of controlling the amount of deposited metal oxide. For the production of acceptable pearl-like pigments, the amount of chromium, vanadium or iron oxide should be at least about 10% by weight of the pigment and may be in the range of up to 30 µm. or even about 50 °. However, suitable amounts of deposited oxide will generally be in the range of about 10 to 30 of the pigment. The actual amount of metal salt used in the solution can often exceed the calculated amount, since it is sometimes difficult to achieve complete depletion of the solutions in the precipitation step within the pH range controlled by the buffer salts used. However, a more drastic increase in pH by the addition of stronger alkaline agents is inappropriate because of the possible precipitation of free metal oxide.

The isolation of these colored pigments from the reaction mixture is also conventional. It is conveniently effected by filtration, washing away of soluble salts and drying at any suitable temperature, e.g. 80 ° C. Such products are valuable pigments, but they can sometimes be improved in stability and changed slightly in color by calcination in air at temperatures which may range from about 300 to 400 ° C for vanadium oxide (VgO₂ melts at 69O ° C) up to about 700 ° C for chromium oxide and iron oxide.

It is also within the scope of the invention that a second layer of metal oxides be deposited on top of or mixed with the titanium oxide or aircon oxide layer. The second layer may be one of colorless oxides such as alumina, zirconia, zinc oxide, tin oxide, antimony oxide and the like or even a second layer of titanium oxide. It may, on the other hand, include oxides which in themselves have color, such as iron oxide, nickel oxide, cobalt oxide, copper oxide or chromium oxide. This second oxide layer apparently changes the thickness of the total oxide layer and thus contributes to the interference phenomenon. It can also contribute with its own intrinsic color along with the interference color, thus obtaining highly unpredictable color effects of great interest.

When depositing a second metal oxide layer on TiO 2 or ZrO₂it may be deposited on either an aqueous titanium or zirconia layer or on the corresponding calcined layer or it may be deposited simultaneously with the titanium oxide layer by the addition of a suitable metal salt to the titanyl sulfate solution. The second layer is generally deposited in lesser quantity than the titanium or zirconia. One of the most remarkable results from the deposition of a second such metal oxide is a marked stabilization of the original aqueous TiO₂photosensitivity of the layer. Alumina is well suited for this purpose. This material has a relatively low refractive index and provides stabilization with a relatively minor effect on the interference color. It is most effectively deposited as a second layer by thermal hydrolysis from a buffered solution such as aluminum acetate.

Other oxides which can be deposited as a second layer include the following:

1st Zinc oxide (ZnO) can be deposited by thermal hydrolysis of an ammoniacal zinc complex solution such as tetramine zinc sulfate. When such a combined layer of aqueous TiO₂ and ZnO is calcined, the resulting layer exhibits the same X-ray diagram as rutile TiO₂, while simple layers of TiO₂ show anatase TiOg. This variation generally seems to have less effect on the properties of the coated flakes.

2nd Zirconia (ZrO₂) can be deposited as aqueous oxide on top of aqueous TiO₂ by thermal hydrolysis of, for example, a zirconium oxychloride solution. It improves light stability with less effect on color. When calcining the combined layers, however, an increase in refractive index occurs, which leads to a color effect to be expected from a thicker layer.

3rd An iron oxide layer (Fe 2 O 3) can be deposited by thermal hydrology of a solution of, for example, iron (III) acetate. The product obtained before calcination is a gold-shiny flake pigment with a distinctive color, which varies with the thickness of the combined layers and is accompanied by a rainbow shimmer. Such pigments impart a distinct two-tone effect to i

compositions containing them. In calcination, a color change towards red occurs in line with the known behavior of the iron oxides, however, to a large extent, the pearl-like effect is maintained.

4th Nickel oxide is easily deposited on aqueous TiC 2 -coated mica by thermal hydrolysis of, for example, a nickel tetramine sulfate solution. The color effects in this case, after calcination, as shown in Example 15, are completely unexpected.

Nickel oxide can also be deposited by thermal hydrolysis of a nickel acetate solution.

5th Cobalt oxide is readily deposited by thermal hydrolysis of a cobalt acetate solution.

6th Some of the most unexpected effects are achieved with chromium oxide (CrgO-j). It is readily deposited by thermal hydrolysis resulting from evaporation of ammonia from a solution in water of a hexamine chromium (II) derivative, or by thermal hydrolysis of a chromium salt solution, buffered with borax. A very thin layer (1-2% C 2 O 2) deposited on an aqueous TiC 2 layer has led to appreciable stabilization of the photosensitivity with very little effect on the color of the pigment. Furthermore, this thin chromium oxide layer appears to stabilize the color during calcination, so that such products are improved in both color and light stability against untreated products.

On the other hand, if a large amount of θΓ2θ3 ~ 15%) is deposited, e.g.

on top of aqueous T1O2, with a gold interference color and the resulting flake pigment calcined, the final product is an attractive, golden, pearl-like pigment with a rainbow shimmer, which lends an interesting two-tone effect to pigmented compositions.

Other unspecified metal oxides can be incorporated into these flake pigments in a similar manner.

The examples of chromium oxide indicated indicate the importance of the thickness variations of the successive layers in multilayer coatings. The amount of titanium oxide or zirconia in the initial layer may vary over the entire range shown for single layers. The colors obtained will have a significant effect on the properties of the final products. Similarly, the second layer can be made to vary in thickness¹play by regulating the amount of reactant used and the deposition conditions. The thickness of the second layer contributes to the interference color in the expected manner, which is subject to variations in refractive index. The invention encompasses intervals in the individual layers of the multilayer coating which are comparable to those of TiO alone.₂·

It is quite clear that the deposition of successive metal oxide layers can be extended beyond two successive layers and the invention also encompasses such multilayer coatings. The invention also encompasses that thick layers of titanium oxide can be deposited in a single step or deposited in successive steps with or without an intermediate calcination step.

The titanyl sulfate solution used in a suitable process for depositing TiO₂, can be obtained in any suitable manner. A relatively pure titanyl sulfate can be obtained by dissolving in sulfuric acid an aqueous titanium oxide precipitate usually obtained as an intermediate in the preparation of TiO₂~ Pigments. However, it has been found that such highly pure solutions are not required and that equivalent results can be obtained by using a standard titanyl sulfate concentrate prepared from the ore which contains a small amount of iron which is held in divalent state by the presence of a small amount of iron. amount of trivalent titanium in the highly acidic solution. Thus, the concentration of the titanyl sulfate in the aqueous solution may vary within a range, e.g. preferably from about 2 'parts (calculated as TiO₂) to about 20 parts per 100 parts solution. Regardless of the concentration, it is necessary that there is free acid in the solution, which always exceeds that required for the transfer of all titanium oxide to TiOSO 4. This is necessary to prevent the precipitation of an aqueous titanium oxide at room temperature. The titanium oxide technique usually uses an acidity factor (FA) as a parameter for defining this relationship, where FA = 100 (total acid - bound acid)

Bound Acid (TiOSÖ /)

The examples below show FA values ​​of about 80 for a concentrated titanyl sulfate solution and about 220 for a more dilute titanyl sulfate. In the range of 50 - 300, 35 are suitable for achieving the best results. The critical condition is that there is sufficient amount of acid to prevent hydrolysis at room temperature but insufficient amount for excessive suppression of the hydrolysis at elevated temperature. The appropriate conditions will apparently vary somewhat with the concentrations of the reactants and with the temperature and within a wide range the conditions can be readily determined by one of ordinary skill in the art. Appropriate FA values ​​are generally within the range considered optimal for the preparation of TiO₂ of pigment quality.

Regardless of the origin of the titanyl sulfate and regardless of the concentration of the starting material, the concentration of the titanium salt in the solution in which the mica is suspended at the hydrolysis point is more diluted by a factor of at least 2 or 3 than is appropriate for Ti0₂-pigment. To obtain the best results of the invention, this titanium salt concentration (calculated as TiO₂) in the solution at the precipitation point should be at least about 2 parts and should not exceed about 7 parts per 100 parts solution.

The amount of titanium (or zirconium) salt used in relation to the mica can vary within a wide range and is important only for controlling the thickness of the final oxide coating. Calculated as TiO₂ (or Zr0₂) should generally be used about 10 parts per 100 parts of mica (about 10 up to as much as about 200 parts per 100 parts of mica (about 66 55) with a preferred range of Ti0₂ of about 15 - 80 parts per 100 parts of mica (about 15 - 40 55 TiO₂). This is of course reflected in the thickness of the deposited layer and in the resulting interference color. It has been found that when the amount of TiC&gt;₂ is in the range of 10 - 26% by weight of the product, a silver colored pigment is usually obtained; in the range 26 - 40/5 the pigment is gold colored and in the range 40 - 50% the color of the pigment varies from red to blue to green as the thickness of the metal oxide layer is increased. In the range 50 - 60% higher order interference colors are obtained. Other methods have also been used according to the invention_;correlation of the film thickness with the interference color. A suitable measure of the thickness of the layer is, for example, the weight Ti0₂, which is deposited per unit area of ​​mica surface (preferably expressed as mg / m 2 mica surface) and may vary from about 50 mg of TiO₂ to 600 mg of TiO₂ or more per surface area. In the upper parts of this range, the observed colors are higher order interference colors. The relationship between the weight of TiO₂ per m and the color varies slightly between uncalcined and calcined products. However, within wide limits, the following table indicates the correlation between observed interference colors and the measured TiO₂~ weight per m mica surface. Since the color shades vary continuously across spectrum, it is clear that the intervals merge at the points of intersection. Pigment with 50 - 280 mg. 2. .

Ten₂ per m mica surface exhibit first-order interference colors and they are the most suitable materials.

<td>Color</td><td>Mg TiO_n per</td>

<td>Silver</td><td> 50 - 100</td>

<td>Gold</td><td> 100. - 180</td>

<td>RED</td><td> 180 - 220</td>

<td>Violet</td><td> 220 - 240</td>

<td>blue</td><td> 240 - 260</td>

<td>Green</td><td> 260 - 280</td>

<td>Gold of the second oath</td><td> 280 - 350</td>

' 2

The weight ZrOg per m will be slightly larger than these values ​​due to the higher density. However, the general principles apply.

Another way to measure TiO₂the thickness of the layer in relation to the color, which way depends on direct measurement and not on prior knowledge of the properties of the mica and TiOg coating, derived from the wavelengths of the interference bands.

In the following table, the optical path has been calculated from measurements of interference bands exhibited by typical products of known composition. Wherever possible, interference bands, either maxima or minima, which fall within the visible part of the spectrum have been used for the calculation. However, silver flakes have no interference bands in the visible spectrum and there is considerable uncertainty about the exact position of the interference band in ultraviolet due to an absorption band for

<td rowspan="3">Ten₂ in the same Weight TiOt, Color</td><td colspan="4">area. The measurements of the thickness are in millimeters 2 per m is in mg and is based on · direct measurements.</td>

<td rowspan="2">Optical path (im µ)</td><td colspan="2">Geometrically thick</td><td rowspan="2">Ten₂ per no (in mg)</td>

<td>play</td><td>(in millimeters)</td>

<td>Silver</td><td>96 (Easter)</td><td> 35</td><td>(Est)</td><td> 85</td>

<td>Pale gold shiny</td><td> 150</td><td> 59</td><td></td><td> 145</td>

<td>Guldglän- Sande</td><td> 175</td><td> 71 '</td><td></td><td> 163</td>

<td>RED</td><td> 250</td><td> 95</td><td></td><td> 186</td>

<td>Violet</td><td> 297</td><td> 117</td><td></td><td> 231 '</td>

<td>blue</td><td> 325</td><td> 129</td><td></td><td> 250</td>

<td>Green</td><td> 358</td><td> 145</td><td></td><td> 275</td>

<td>Gold shining of the second order</td><td> 412</td><td> 161</td><td></td><td> 320</td>

<td>Violet of the second order</td><td> 487</td><td> 194</td><td></td><td> 385</td>

/

<img file="SE320135B_D0002.tif" />

From these values ​​it can be seen that products of technical value exist in the entire range from about 30 to 200 millimicrons in the calculated geometric thickness of the oxide layer. It has been found in other studies that a wider range of about 20 millimicrons - about 250 millimicrons is also useful, with the range of about 20 - 155 millimicrons for first-order interference colors being most suitable.

The following table shows the colors obtained in different thickness ranges.

Color

Geometric thickness range (in millimeters)

Silver

Pale gold shiny

SHINING LIKE gOLD

Red Violet

blue

Green

Gold of the second order Violet of the second order

- 40 (

(40 - 90 (

- 110 110 - 120 120 - 135 135 - 155 155 - 175 175 - 200

The thickness of a ZrOg layer may vary slightly from the values ​​given, as ZrO₂ has a significantly lower refractive index.

The insulation of TiO₂The pigments according to the invention by filtration, washing and drying are quite conventional. However, it is well known that a certain amount of sulfate ion is very rapidly retained by an aqueous titanium dioxide precipitate. It is sometimes convenient to promote a complete removal of this sulfate by washing with a dilute alkali solution, such as diluted ammonium hydroxide either on the funnel or by re-slurrying in such a solution, sequentially, by filtration and new washing.

The new compositions provide a hitherto unknown family of colored, pearl-like flake pigments, which are relatively free from random light scattering and derive their color solely from the optical interference phenomenon when the layer is selected from a colorless titanium or zirconia. When another adhesive, luminous layer of a second metal oxide, which itself may be colored, is deposited on or mixed with the titanium oxide (or zirconia), coated flakes, new products with an increase in color and improvements in other properties are obtained. The use of colored metal oxides of iron (III) oxides, chromium (III) oxide, vanadium (V) oxide and aqueous oxides of iron (III) and chromium (III) gives a hitherto unknown family of colored, pearl-like flake pigments, which are likewise relatively free from random light scattering and exhibiting ice 320135 both the metal oxide's own color and a reflex color resulting from the optical interference phenomenon. Dispersed in the usual manner as pigments in various systems, the compositions exhibit new color effects, which include a shiny pearl-like sheen, the metal oxide's own color and a layered, glossy, pearl-like luster. Viewed under the mirror angle under bright light, such as sunlight, they exhibit a striking rainbow shimmer on a background of a predominant color. When the oxide coatings are all in themselves colorless, the observed color is solely the result of optical interference and varies in hue from a silvery pearl shimmer · over gold and red to blue and green as the thickness of the combined oxide layers increases. When a colored oxide is coated on a titanium or zirconia layer, both the inherent color of the other oxide and the interference color of the combined layers can be observed as a variety of effective effects.

The aqueous iron oxide coatings according to the invention are golden yellow and, when calcined, turn to brown and finally to red. Aqueous chromium oxide coatings are greenish and change upon calcination to lighter green. Aqueous oxide-treated products containing vanadium are brownish gray and change upon calcination at 300 - 400 ° C to glow bright yellow.

A very unusual and unexpected aspect of the present invention is the limited range of only three colored metal oxides (chromium vanadium and iron) which can be deposited solely as layers directly on mica flakes and can be maintained in the particle size range required to produce a pearl like nature of the products. It has been found that many metal oxides can be deposited on mica, which has been previously treated with a layer of titanium or zirconia. However, it was completely unexpected to find that of these oxides, only the iron (III), chromium (III) and vanadium (V) oxides could be used directly on the mica to produce interference effects.

When a colored oxide is present, the new pigments, in addition to the oxide's own color, exhibit interference colors of the specified shades. Such colors are often referred to as reflex colors. They are quite indeterminate, and are best observed under certain specified conditions. Bulk powders generally show only the colors of the metal oxides. If the powder is spread in a thin layer, e.g. slightly between the fingers and observed in 'clear sunshine, it can show a distinct sparkle with signs of the reflex color in addition to the color of the oxide. If mixed with water on a 'black surface', the interference color and sparkling become immediately visible.

Dispersed in carriers for coating compositions, plastics and the like, the reflex color is best observed at the angle of reflection under strong lighting, such as in sunshine. Since this color generally differs from the intrinsic color of the oxide, effective two-tone effects are often achieved.

With respect to iron, chromium and vanadium oxides, the hue of the interference dye is a function of the thickness of the oxide film and follows the general rules stated. Another measure is the actual weight percent of the metal oxide, based on the weight of the final pigment. This can range from about 10 to about 40, preferably about 10 to 30. For the smaller amounts of metal oxide, e.g. from about 10 to about 20%, the reflex colors are generally silver-like and become gold-shiny when the amount increases beyond about 20%. There is no arbitrary upper limit on the amount of metal oxide that can be deposited, but practice shows that amounts in excess of about 30 l = are difficult to deposit and that about $ 40 is a limit in practice.

It seems that one of the critical characteristics that distinguishes them. new products from known pigments lie in the properties of the metal oxide deposited on the mica flakes. Examination of such flakes in the electron microscope both before and after calcination suggests that water-containing oxide layers have such small particles that they dissolve very poorly in the electron microscope. They are not completely non-crystalline, because they have distinguishable X-ray diffraction diagrams and there are some signs of very small particles, on the order of 0.01 microns, but these particles do not appear to have sharp edges and tend to be irregular in size and shape. . When calcined, a definite, crystalline pattern becomes evident, but for products that are pearl-like, the crystallites are extremely small and tightly packed, so that the optical character is a film.

Measurements of TiO₂The particles show a maximum particle size of about 0.1 micron for all calcination temperatures below about 1000 ° C, in a suitable calcining temperature range for Ti₂ from 7Q0 to 1000 ° C, substantially all particles are less than 0.1 micron in diameter. At higher temperatures, some larger particles appear, and when the particles of Ti0₂ or another oxide substantially exceeding 0.1 microns in diameter, the product's interference colors and pearl-like properties are no longer evident. Such products exhibit the light scattering properties of ordinary TiO₂ or in other pigments.

Measurement of chromium, vanadium and iron oxide particles show a maximum particle size of about 0.1 micron. However, there seems to be some limit to the temperature above which the particles grow to substantially larger sizes than 0.1 microns and when this occurs the pearl-like properties disappear. The maximum permissible temperature differs for these three oxides and is about 800 ° C for iron oxide, about 700 ° C for chromium oxide and about 500 ° C for vanadium oxide. Such larger particles exhibit the light-scattering properties of ordinary metal oxide pigments.

In discussing the properties of these new pigments, emphasis has been placed on compositions in which they are used individually. However, they can be used in mixtures with other pigments. With black pigments, such as carbon black, there is often some increase in the effect of the reflex paint. In mixtures with ordinary colored pigments with comparable shades, the pearl-like properties are maintained and often the sparkle, while the effect on the color is often unpredictable. Many combinations have an effect similar to aluminum flakes without many of the disadvantages of aluminum flakes.

When the new flakes are used in admixture with common high-pigment pigments, such as TiOg pigments, pronounced pearl-like or pearl-like properties are quite evident, even with as much as 25-50 $ TiC 2, but the rainbow-shimmering sparkle can be greatly diminished. Nevertheless, such mixtures offer attractive possibilities.

An outstanding feature of the new flake pigments is their remarkable ease of dispersion in carriers for coating compositions. In virtually all known pigments, it has been considered necessary to subject them to significant grinding action to achieve the required dispersion degree in the preparation of high quality paints, varnishes and the like. Metal oxide pigments generally require significant painting to provide acceptable varnishes. Mica also requires considerable work on the system for good dispersion. Therefore, it is totally unexpected to find that the new pigments, whether calcined or not, can be dispersed in a large variety of carriers by simple vigorous stirring. Further painting shows little if any advantage and can easily be carried out to the point where the flakes are broken with an inappropriate effect on the color obtained.

These new pigments have their principal value as constituents of such compositions as paints, inks, plastics films, rubber articles and the like, which impart color and other decorative effects and on which they often exert a profound effect on the durability of such compositions upon exposure to the atmosphere. When referring to the color and decorative properties of the pigment 40, it is generally understood that reference is made to compositions containing the pigments and the following are typical but not limiting.

Preparation A.

Unbound film on cellulose acetate.

1.0 part of pigment is added to 20 parts of a cellulose acetate solution containing 16.7 liters of cellulose acetate in acetone. The mixture is stirred until thoroughly mixed. A glass plate is prepared for stripping a film therefrom by coating the clean sheet with a silicon grease-type crane grease and then rubbing it thoroughly with a clean cloth.

The varnish is spread on the glass plate and drawn down to a thickness of the * wet film of about 0.16 mm. After the solvent has evaporated, the film is stripped from the wafer and observed on the smooth side. Such films are suitably used for light fastness, testing in a Padeometer.

Preparation B.

Hardened acrylic paint.

2.5 parts pigment

17.9 parts mixed acrylic ester polymer (Acryloid A 101-Rohm and Haas)

7.7 parts butyl benzyl phthalate

20.0 parts of monoacetate of ethylene glycol monoethyl ether

56.9 parts of methyl ethyl ketone 50.0 parts of toluene.

The pigment is dispersed by vigorously stirring the resin and plasticizer together with some of the solvents for about 15 minutes; the remainder of the solvents are then added and the mixture is continued to uniform. Samples are prepared by spraying on primed panels, then dried and cured for 20 minutes at 80 - 85 ° C. As a quick test method, alternatively films of this varnish can be spread to uniform thickness with a scraper and observed after air drying.

Preparation C.

Hardened alkyd lacquer.

2.5 parts pigment

29.2 parts non-oxidizing coconut oil - modified alkyd resin solution ($ 60 dry substance)

13.6 parts modified melamine formaldehyde resin (55% dry substance)

15.0 parts of aromatic hydrocarbon solvent,

19.0 parts of aliphatic hydrocarbon solvent.

The pigment is added to the mixed resin solutions together with a portion of the solvent and dispersed by stirring at high speed for about 15 minutes, after which the residual solvent is stirred. The resulting varnish is sprayed onto a primed metal plate and cured for 0.5 hours at about 120 ° C. Films of uniform thickness can also be applied with a maker.

Preparation D.

Vinyl Plastic Film.

<td colspan="2">3 parts</td>

<td> 100</td><td>parts</td>

<td> 40</td><td>parts</td>

<td> 10</td><td>parts</td>

<td> 3</td><td>parts</td>

<td> 0,22</td><td>parts</td>

pigment vinyl chloride polymer dioctyl phthalate polyester resin stabilizer (barium-cadmium-zinc phosphite) stearic acid.

The pigment is added to the mixture of the ingredients and the whole mixture is treated on a two-roll mill and heated to 155 ° C until uniform. It is finally taken from the rolling mill as a sheet. of any desired thickness; the sheet may be observed in the obtained form or may be press-polished in a suitable heated press.

These compositions are all common and can be modified in well-known ways or can be replaced with equally common compositions, including cellulose nitrate varnish, linseed oil varnish or other oil resin varnishes, linoleum compositions, rubber, polyethylene resins and the like.

In all cases, the observed color can be confirmed by optical measurements, such as spectrophotometric reflection curves, which can be determined by measurements of dispersions of the colors over non-reflective backgrounds.

Such measurements give reflection curves that correspond to the observed color. As the oxide coating itself is colorless, there is a progressive transition to longer wavelengths for reflection minima as the thickness of the coating increases. In a series of tests with increasing amounts of TiO₂ in a single coating, for example, vary the wavelengths of the minimum and maximum reflection values ​​for typical samples with the color of

<td colspan="4">the following ways:</td>

<td></td><td>Wavelength too</td><td colspan="2">first interference band.</td>

<td>Color</td><td>Minimum</td><td>• Maximum</td><td></td>

<td>Silver</td><td>In ultraviolet</td><td>about 390</td><td>millimicrons</td>

<td>Gold</td><td>390 millimicrons</td><td> 700</td><td>t '</td>

<td>RED</td><td> 500 </td><td> 970</td><td>t</td>

<td>Violet</td><td> 570</td><td> 1100</td><td>u</td>

<td>blue</td><td> 600 </td><td> 1170</td><td>t</td>

<td>Green</td><td> 685 </td><td> 1350</td><td>it</td>

The second interference band

<td>Color</td><td>Minimum</td><td>Maximum</td>

<td>Gold (other words)</td><td>430 millimicrons</td><td>550 millimicrons</td>

<td>solution)</td><td></td><td></td>

<td>Violet (second order)</td><td> 500 </td><td> 650 </td>

Here, a multilayer coating contains an oxide, which itself is colored, shows the spectrophotometric curve of both the self-color absorption band and the interference bands due to the film on the luminous flake pigments.

Example I.

580 portions of an aqueous titanyl sulfate solution containing

4.4% TiO₂ such as titanyl sulfate (equivalent to 25 parts of TiO₂) and has an FA of 217, diluted with 500 parts of water. 100 parts of mica are then suspended in this solution. The mica is a water-milled, white shiny 15 more (muscovite) named COWCORD WET GROUND MICA no. 200/325. This p

mica has a specific weight of about 3.3 m / g, as determined by krypton adsorption according to the predetermined B.Ε.T. method; all mica passes through a 200 mesh screen and about 94%. through a 325 mesh screen. The average particle size is in the range of 20 - 40 microns at maximum dimension and about 0.1 microns in thickness. The mica suspension in the titanium sulfate solution is heated rapidly (about 10 minutes) to boiling and kept under reflux for about 2.5 hours. The product is isolated by filtration and washed with water to pH 5.0. After drying at 80 ° C, about 135 parts of a finely divided flake pigment is obtained, which does not require any further particle size reduction. In bulk, this flake pigment is a shiny, slightly yellow powder. It can be easily dispersed in various carriers for coating compositions by simple stirring at high speed. Dispersed in an alkyd resin support, such as in formulation C, and coated on a black, grounded metal surface, the resulting surface has a silver-like appearance and a brilliant rainbow shimmer in the sunshine.

Example Ia.

This part of the example illustrates how a color change can be achieved by using a greater amount of titanyl sulfate solution, thus depositing a thicker layer of aqueous TiO₂.

If the procedure of Example I is followed, except that the amount of titanyl sulfate solution is increased to 1160 parts (50 parts of Ti0₂), the flake pigment yield becomes about 150 parts of a shiny powder with a slightly more yellowish color change. Dispersed in the alkyd resin support and coated on a black primer, a golden appearance and an appealing, shiny rainbow shimmer are achieved, especially when viewed in the sunshine.

Example II.

The mica used in this example has a larger particle size than the one used in Example I. It was obtained by sieving the mica in the previous example and collecting the portion passing through a 200 mesh screen and retaining it on a 325 mesh screen.

100 parts of this -200 / + 325 mesh mica are slurried in 1160 parts of titanyl sulfate solution of Example I and the mixture is treated in the manner described in this example. on the mica flakes than obtained in Example Ia. When the flakes are dispersed in a carrier for a coating composition and laid over a black surface, a blue appearance and an appealing, glossy sparkle are obtained.

By using specified conditions and even larger mica flakes which pass a 160 mesh screen but are retained on a 200 mesh screen, the result of the smaller surface becomes an even thicker coating of aqueous titanium dioxide. When such flakes are incorporated into a coating composition carrier and placed on a black surface appears a gold color and an appealing glossy sparkle. The golden appearance obtained with this thicker layer of aqueous titanium dioxide is a second-order interference color.

Example III.

According to the precipitation procedures of Examples I and II and in this example, mica flakes are coated with a luminous layer of aqueous titanium oxide. This example further illustrates the variation in color with the variation in TiO 2 content per unit area along with the changes that occur in calcining the pigment to transfer the aqueous oxide coating to a more light stable, luminous coating of titanium dioxide.

A number of experiments were performed using the amounts of titanyl sulfate solution and mica indicated in the following table. The mica used and the titanyl sulfate solution were the same as those described in Example I. All quantities are expressed in parts by weight. The mica is dispersed in the titanyl sulfate solution and the resulting mixture is heated to boiling and refluxed for 3 hours, after which the product is isolated by filtration, washing and drying in the manner described in Example I. The dry product is then calcined in air for 1 hour at about 95 ° C. Upon cooling, shiny flakes with rainbow shimmer are obtained. In bulk, both the · calcined and the uncalcined products can be described as discolored white. Dispersed in a liquid and observed on a dark surface, however, they are observed in the table

<td> 320135</td><td> 22</td><td></td><td></td><td></td>

<td>given the colors. These colors shimmer flakes:</td><td>vary</td><td colspan="2">with the amount of TiO₂~</td><td>coating on</td>

<td>Mica</td><td> 100</td><td>1-0G</td><td> 100</td><td> 100</td>

<td>Titanylsulfatlösning</td><td> 772</td><td> 1160</td><td> 1600</td><td> 2440</td>

<td>Equivalent TiO₂</td><td> 33</td><td> 50</td><td> 70</td><td> 105</td>

<td>Yield - uncalcined</td><td> 135</td><td> 155</td><td> 178</td><td> 210</td>

<td>Hydrated TiO₂/ m² g</td><td> 0,11</td><td> 0,17</td><td> 0,24</td><td> 0,34</td>

<td>Color</td><td>Bleached gold</td><td>dark gold</td><td>Bluish violet</td><td>Pale gold second order</td>

<td>Yield after calcination</td><td> 17-3</td><td> 140</td><td> 156</td><td> 182</td>

<td>Ti0₂/ m² g</td><td>O ', Ø85</td><td> 0,14</td><td> 0,19</td><td> 0,27 .</td>

<td>Color</td><td>Very bleached</td><td>Medium gold</td><td>gold Red</td><td>Green</td>

The table shows that there is a weight loss at TiO₂coating on calcination. Such a loss is of course accompanied by some reduction in the thickness of TiO₂film and a change in the predominant hue of the colors. This change is in the direction of interference at a smaller wavelength, as expected by thinner films. The calcined products of this example are much more light stable than the uncalcined products of Examples I and II.

Example IV.

This example illustrates coating of mica flakes using a concentrated titanyl sulfate solution of the type usually prepared during the transfer of ilmenite ore to TiO.₂-pigment. Although such solutions usually contain some iron in divalent form, this is not precipitated together with aqueous TiOg. Instead, the iron remains dissolved as FeSOO in the mother liquor.

As detailed in the following table, 100 parts of mica as described in Example I are slurried in the amount of water and heated to about 60 ° C. With vigorous stirring at 60 ° C, rapidly indicated amount of concentrated titanyl sulfate solution (TiOSO₂), calculated as TiO₂, 14.1 FeSO 1, calculated as Fe, 3.7 FA - 80), which is also heated to 60 ° C. The mixture is heated to boiling and the boiling is continued under reflux for the specified time. The flakes are recovered by filtration, washed free of soluble salts and dried at 80 ° C. The slightly yellow, pearl-like flakes are then calcined in air for 1 hour at 950 ° C to obtain slightly darker colored flakes dispersed in coating compositions to impart specified colors to the compositions together with a shiny rainbow shimmer in the sunshine.

<td></td><td>23rd « A</td><td>B</td><td>v lud</td>

<td>Mica</td><td> 100</td><td> 100</td><td></td>

<td>Water</td><td> 236</td><td> 448</td><td></td>

<td>Titanylsulfatlösning</td><td> 190</td><td> ' 365</td><td></td>

<td>Equivalent TiO₂</td><td> 27,3</td><td> 52,3</td><td></td>

<td>Äterflödeskokningstid</td><td>2 hours</td><td>2.5 hours</td><td></td>

<td>Exchange</td><td> 130</td><td> 165</td><td></td>

<td>% aqueous TiO₂</td><td> 23,1</td><td> 39,4</td><td></td>

<td>Yield after calcination</td><td> 127</td><td> 148</td><td></td>

<td>% TiO₂</td><td> . 21,4</td><td> 35,4</td><td></td>

<td>Color</td><td>Silver</td><td>Gold</td><td></td>

<td>The interference color of</td><td>Example V. one coated</td><td>flake pigment is one</td><td>function of</td>

<td colspan="2">the thickness of the coating layer thereon.</td><td>Because real</td><td>measurements of</td>

while this layer is not readily performed, the weight of the coating material per unit area of ​​substrate is a suitable index of the thickness of the coating. It is clear that a certain weight of coating material will yield coatings of different thicknesses on equal weight amounts of substrate which differ in surface area. However, such adjustment of the substrate weight, that the total surfaces are equal, should give the same coating and substantially the same color. The following test series illustrates this by using three samples of water-painted white mica (muscovite) with the weights so adjusted that the total surface area of ​​the mica used is equal in the different cases.

The titany sulphate solution had the following composition: TiOSO 2, calculated as TiO₂, 14.1 FeSO 2, calculated as Fe, 3.7 Nk - 80. The general procedure used for coating the mica is described in Example IV. Details of the procedure are as follows:

Surface and weight of samples.

<td></td><td>Sample 1</td><td>Sample 2</td><td>Sample 3</td>

<td>O The surface of the mica, m / g</td><td> 3,2</td><td> , ²’⁶</td><td> 2,4</td>

<td>The weight of the mica used</td><td> 20,0</td><td> 24,6</td><td> 26,7</td>

<td>• 2 The total surface of the mica, m</td><td> 64,0</td><td> 64,0</td><td> 64,0</td>

<td>Treatment:</td><td>. Sample 1</td><td>Sample 2</td><td>Sample 3</td>

<td>a. The weight of TiOSO 2 (calculated as TiO₂) g</td><td> 11,7</td><td> 11,7</td><td> 11,7</td>

<td>Exchanges ig</td><td> 29,9</td><td> 34,2</td><td> 36,4</td>

<td>The weight of hydrated TiO₂ on</td><td></td><td></td><td></td>

<td>coated flakes</td><td> 9,9</td><td> 9,6</td><td> 9,7</td>

<td>Hydrated TiO₂/ m² mica eye g</td><td> 0,16</td><td> 0,15</td><td> 0,15</td>

<td>Interference color - all three equal</td><td></td><td colspan="2">Bright gold colored</td>

<td>b. Weight of TiOSO 4 (calculated as TiO₂) g</td><td> 15,6</td><td> 15,6</td><td> ' 15,6</td>

<td>Exchanges ig</td><td> 33,1</td><td> 37,0</td><td> 39,9</td>

<td colspan="2"></td><td>Sample 1</td><td>Sample 2</td><td>Sample 3</td>

<td></td><td>Weight of hydrated TiO₂ on coated flakes</td><td> 13,1</td><td> 12,4</td><td> 13,2</td>

<td></td><td>Hydrated TiO₂/ m sparkle ig</td><td> 0,20</td><td> 0,19</td><td> 0,21</td>

<td></td><td>Interference color - all three equal</td><td colspan="3">Reddish gold</td>

<td> 5</td><td>c. Weight of TiOSOjj (calculated as TiO₂) g</td><td> 19,5</td><td> 20,8</td><td> 20,8</td>

<td></td><td>Exchanges ig</td><td> 36,5</td><td> 41,5</td><td> 43,6</td>

<td></td><td>Weight of hydrated TiO₂ on coated flakes</td><td> 16,5</td><td> 16,9</td><td> 16,9</td>

<td></td><td>Hydrated TiOg / m 2 mica ig</td><td> 0,26</td><td> 0,26</td><td> 0,26</td>

<td></td><td>Interference color - all three equal</td><td></td><td>blue</td><td></td>

<td> 10</td><td>Example</td><td>WE.</td><td></td><td></td>

<td></td><td colspan="2">In an examination of the particle size</td><td>at TiO₂, deposited</td><td>On</td>

mica flakes, a sample of uncalcined, silver-colored flake pigments can be prepared as follows, which differs only in detail from the sample A of Example IV.

O

100 parts of water-ground, white mica (surface 3.2 m / g) are slurried in 1000 parts of water and the slurry is heated externally to about 95 ° C. At this point, 290 parts of a titanyl sulfate concentrate (15% available TiO) is rapidly added₂ ~ FA 80) quickly to the stirred slurry. The resulting slurry (temp. 89 ° C) is heated to boiling and boiled for 1.5 hours, cooled to 60 ° C, filtered, washed free of sulfate ion and dried to give 135 parts of a yellowish, β

pearl-like silver pigments. Parts of this pigment are then calcined in air at various temperatures, as shown in the following table. The final flakes are then examined after calcination in the usual way in an electron microscope and the overall appearance of the samples and an estimate of the average particle size are shown in the table. Three other samples, similarly prepared and examined¹similar methods in electron microscope are included in the table.

<td>Sample</td><td></td><td>The calcination temperature</td><td>General appearance</td><td>particle Size (Microns)</td>

<td colspan="2">This</td><td>uncalcined</td><td>Undetermined particles,</td><td>Not measurable</td>

<td colspan="2">example</td><td></td><td>very small</td><td></td>

<td> 11</td><td></td><td>700 ° C</td><td>Uniform, separate particles</td><td> 0,025</td>

<td> 11</td><td></td><td>900 ° C</td><td>n</td><td> 0,04</td>

<td> 11</td><td></td><td>1000 ° C</td><td> 11</td><td> 0,09</td>

<td>n</td><td></td><td>1100 ° C^x</td><td>^: Many rib-like particles of uniform size</td><td> 0,10</td>

<td>Sample</td><td>A</td><td>95o ° C</td><td>Separate particles</td><td> 0,08</td>

<td>Sample</td><td>B</td><td>900 ° C</td><td>Separate particles</td><td> 0,03</td>

<td>al</td><td> 11</td><td>95o ° C</td><td>II »</td><td> 0,07</td>

<td>Sample</td><td>c</td><td>85o^qC</td><td>Separate particles</td><td> 0,04</td>

<td>II</td><td> 11</td><td>950 ° C</td><td> « 11</td><td> 0,07</td>

^xIt should be noted that at temperatures of about 1100 ° C and above, the mica begins to decompose and the crystal growth of TiO₂ will be much faster.

Example VII.

This example illustrates the use of an organic titanate for applying a titanium oxide layer to mica flakes.

About 1 g of mica flakes (muscovite) with the largest dimensions about 100 microns and with a thickness of 1 - 2 microns are spread in a thin layer on the inside of a 2.5 cm VYCOR tube. The tube is evacuated by means of a vacuum pump attached to one end of the tube, the other end of the tube via a closed valve.⁵ is attached to a container of tetraisopropyl titanate contained in a glass flask. The contents of the tube and the piston are heated to 600 ° C while maintaining the vacuum at which temperature the valve between the tube and the container of organic titanate is opened, allowing the titanium vapors to pass into the hot tube. After about 30 minutes, the valve and tube containing are cooled to room temperature under vacuum. After cooling, the vacuum is turned off and the coated flakes are removed from the tube. The obtained flakes exhibit a variety of interference colors and, when dispersed in a cellulose acetate film, give it a pearl-like appearance.

Example VIII.

This example illustrates the improvement in light stability of aqueous titanium dioxide coating by the application of an outer coating of aqueous alumina to the TiO₂-coated mica flakes.

100 portions of the yellowish white flakes of Example Ia are neutralized by slurry in excess dilute aqueous ammonia. They are then filtered, washed and possibly dried and slurried again in 4000 parts of an aqueous solution containing 200 parts

al₂(SO |) J.I8H2O and 80 parts of sodium acetate. The slurry is heated to 90 ° C and then held in the temperature range 90 - 100 ° C for about 30 minutes. The slurry is filtered hot, washed with warm water until it is free of sulfate, and dried at about 60 ° C to give a powder containing about 6 $ alumina (such as

al₂0 +). This powder is more yellowish than the starting material and when dispersed in an alkyd coating composition, such as preparation D, and applied over a black primer, a dark golden, pearl-like appearance and a glossy rainbow shimmer are achieved. Tested in a PADE-OMETER, a cellulose acetate film (such as in Preparation A) shows pig40 mentored with these flakes, a marked superiority in light stability to the untreated sample.

Example IX.

This example illustrates yet another enhancement in light stability by applying a layer of aqueous alumina to a calcined TiO₂ coated mica flake pigment,

100 parts of the calcined product of Example III obtained from the use of 100 parts of mica and 772 parts of titanyl sulfate solution are mixed with 200 parts of aqueous solution containing 20 parts of Al₂O. And 5^_Percent solution of sodium carbonate was then added slowly with stirring until pH is 7.0. The Fling10 pigment is then isolated by filtration, washed free of soluble salts and dried. The product obtained is substantially unchanged with respect to sparkling and totally silver-like gold appearance, when dispersed in a carrier for a coating composition and applied over a black surface. It, on the other hand, shows a remarkable improvement in light fastness. Cellulose acetate films containing the pigment show no change in exposure in an Atlas FADE-OMETER for 1000 hours.

Example X.

This example illustrates the use of synthetic phlogopite as a mica flake substrate.

parts of synthetic phlogopite of such a particle size that everything passes through a 160 mesh screen and retained by a 200 mesh screen is added at room temperature (about 25 ° C) to 600 parts aqueous titanyl sulfate solution containing 24 parts of titanyl sulfate, calculated as

TiO 2, and has an FA of 217. The mixture is stirred and diluted with 600 parts of water and then heated to 80 ° C for 1 hour and held at 70 - 80 ° C with vigorous stirring. Parts of the slurry are occasionally removed and placed in a water stain · on a black surface to determine the color. After about 1.5 hours at 70 - 80 ° C a blue color becomes clear.

With continued stirring for a total of 3 hours, the color of samples taken during the stirring time becomes successively gold-colored, red, blue, green, gold-colored (again), red (again) and then finally green. The slurry is then filtered and the filter cake washed with water until the effluent wash water gives a negative test for sulfate ion.

The filter cake is then washed with acetone and allowed to dry. The end product is a flake pigment with a predominantly green hue and a shiny rainbow shimmer when the pigment is dispersed in an alkyd resin and considered in sunshine.

Example XI.

This example illustrates the application of an aqueous zirconia to mica flakes.

100 parts of mica, described in Example I, are slurried in 2000 parts of aqueous solution containing 200 parts of Zr (SO 2)₂.4H₂O and stitch is preset to pH 2.8 by the addition of urea. The slurry is heated to 90 ° C and kept close to this temperature for about 2 hours with good agitation. The solid product is recovered by filtration, washed and dried and then calcined for 1 hour at 700 ° C in air to obtain a flake pigment having a silver-like appearance and an attractive, glossy sparkle when the pigment is dispersed in a coating composition carrier.

Example XII

.................... 0

This example illustrates the application of a layer of aqueous zinc oxide to mica flakes previously coated with TiO._2&lt;

The procedure of Example Ia is followed for the preparation of TiO₂-coated mica flakes and before drying 30 parts of these flakes are slurried into 2200 parts 3^-percent aqueous ammonium hydroxide solution at room temperature. The mixture is stirred for 30 minutes at room temperature and then filtered. The press cake is washed with water until the pH of the flowing wash water is 8, and then dried in an oven at 80 ° C.

parts of the dried flakes are added at room temperature to a solution formed as follows: 10 parts of ZnCl₂ dissolve in 500 parts of water and ammonium hydroxide is then added to the solution with vigorous stirring until the originally formed precipitate is dissolved again. The slurry is heated to about 80 ° C and maintained at about this temperature for about 2 hours to evaporate the ammonia from the solution. After heating, the slurry is filtered and the cake is washed free of soluble chlorides and dried at about 80 ° C. The resulting product has to a great extent the same appearance as the product of Example Ia. Analysis shows the presence of $ 19 zinc, calculated as zinc oxide. The light fastness of the zinc treated product is significantly superior to the light fastness of the corresponding product without zinc treatment. Calcination of this zinc-containing product gives a flake pigment, in which TiO₂ is presently predominantly in rutile form, while in the corresponding calcined flake product, which is not zinc treated, TiO₂ predominantly have anatase structure.

Example XIII.

This example illustrates the application of a layer of aqueous zirconia to mica flakes which have been coated with TiO 2 in advance.

A TiO₂Coated mica flake pigments, which show gold color when observed on a black surface, are prepared as follows: 108 parts of water ground muscovite mica with a surface area of ​​3.1 iu / g are slurried in 600 degrees of water. The slurry is heated to boiling and 351 parts of a 20 percent (such as TiO₂titanium sulfate solution (FA 80) is added to the boiling slurry. The heating is continued and the mixture is refluxed for 3 hours and allowed to cool overnight before filtration.

After filtration, the press cake is washed with about 12000 parts of water at room temperature, then washed with about 500 parts of 2% ammonium hydroxide solution and finally washed with 6000 parts of water. After drying the press cake overnight at 80 ° C, 164 parts of flake pigment containing about 34 liters of aqueous titanium oxide are obtained. Dispersed in a carrier for a coating composition, these flakes exhibit a reddish gold color which is more pronounced over a dark surface.

. 50 parts of these golden flakes are then coated with aqueous zirconia as follows: 7.5 parts Zr (SO 2 |)₂.4H₂O is dissolved in 500 parts water and urea is then slowly added to solution under good stirring to achieve pH 2.0. 50 parts of golden flakes are added to the solution, the resulting slurry is heated to, boiling and kept for 1 hour under reflux. When heated, the original gold color of the flakes will eventually turn to a purple color. Addition of more zirconium sulphate urea solution and further heating results in a gold color al the second order of the flakes. The slurry is then filtered and the solid is washed free of sulfate and dried to obtain a pigment which has a golden color when dispersed in a coating composition support and applied over a black surface. Accelerating light fastness tests show that the zirconium coated flakes are significantly better in light fastness than the uncoated ones. They contain about 7.7? zirconia (such as ZrO₂).

The following Examples XIV - XVII are based on the use of TiO₂Coated mica flakes which are prepared according to the general procedure of Example IV and which are additionally coated with a second metal oxide, as will be shown in more detail. In these examples, two different samples are shown: one of these samples (flakes A) is an uncalcined, silver colored flake containing about 20.7% TiO₂This product was prepared by treating 100 parts of mica as described in Example 35, with 233 parts of a titanyl sulfate concentrate containing 15 1&gt; TiO₂ (FA about 80) (which is equal to 35 parts of TiO₂). The method used is according to Example IV and about 126 parts of flakes are obtained.

Prior to drying, residual sulfuric acid is neutralized by slurry in excess dilute ammonia, after which it is filtered and washed. The second sample (flakes B) is a yellowish, silver colored flake containing about 26.2% TiO₂ and similarly prepared from 100 parts of mica as described in Example I, and 290 parts of titanyl sulfate concentrate (FA, about 80) containing 55 TiO2, which is equal to 43.5 parts of TiO₂·

In Examples XIV - XVIII, the term reflex color refers to the color observed at the angle of reflection and which is usually in contrast to the own color. This expression is thus a convenient way to distinguish the interference color from the metal color of the metal oxide coatings.

Example XIV.

This Example and Example XlVa illustrate the application of a chromium oxide layer to mica flakes which have been coated with TiO in advance.₂·

Crd 2 H 2 Cl 2 is prepared by dissolving 40 parts CrCl 2 in liquid ammonia, after which the excess ammonia is allowed to evaporate.

The thus obtained light green product is dissolved in 2000 parts of water and then stirred with 100 parts of TiO₂-coated mica (flakes A). The slurry is heated to boiling and refluxed for about 4 hours until the green color of the solution no longer appears. The product is then isolated by filtration, washed with water and dried. The flake pigment product is light green in color and at the same time this green color has a silver-like reflex.

When calcined at 950 ° C, the green color becomes slightly less intense, but the silver reflex is maintained. This product containing chromium oxide equivalent to 3.0¹% Cr, is noticeably more light-resistant than the untreated flakes A.

Example XIVa.

100 parts yellowish silver flakes B (26.2% Ti0₂) is slurried in a solution of 40 parts of chromium sulphate (Cr₂(SO |) +. 5H₂O) in 1000 parts of water at about 50 ° C. Borax (NagB ^ Oy.10H₂0) is then added in small portions of about 2 parts each until a constant pH of 5.5 - 6.0 is reached, after which this pH is maintained for at least 15 minutes. The resulting product is isolated by filtration, washed sulfate-free and dried. After calcining for 0.5 hours at 900 ° C, the flakes are greenish gold colored with a golden reflex and they exhibit excellent lightfastness in the cellulose acetate film of Preparation A.

Example XV.

This example and Example XVa illustrate the application of an iron oxide layer to mica flakes which have been coated with TiOg in advance.

400 parts silver colored flakes A (20.7% TiO₂) is added to a solution of 50 parts of iron (III) chloride (FeCl 2) and 80 parts of sodium acetate (NaC).₂of H₂) in 1000 parts of water at 25 ° C. The slurry is heated with stirring to 80 ° C and stirred for 1 hour at 80 ° C until the mother liquor is essentially colorless. A further portion of the solution containing 50 parts of iron (III) chloride and 80 parts of sodium acetate in 1000 parts of water is then added. The mixture is heated for 1 hour at 80 ° C, after which an additional 50 parts of iron (III) chloride and 80 parts of sodium acetate in 1000 parts of water are added and the whole mixture is heated for 1 hour at 80 ° C. The slurry is filtered, washed and dried, yielding yellowish brown flakes with a golden reflex. When calcined at 400 ° C, 600 ° C and 900 ° C, keeping the pigment 0.5 hours at each temperature, the golden reflex does not change, but the total color changes to brown at 400 ° C, to reddish brown at 600 ° C and to brilliant golden brown at 950 ° C ·

Example XVa.

100 parts of the yellowish silver flakes B (26.2 TiO 2) are added to 600 parts of an 11.4% FeCl 2 solution (68 parts FeCl 2) and 60 parts of sodium acetate (NaC 2 H 2 O 2) are added with stirring. After the sodium acetate is dissolved, the slurry is heated to 80 ° C and kept for several hours at this temperature under the frequent examination of a diluted drop of the slurry on a black surface. The total color of the flakes is golden yellow and the colored sparkle or reflex color goes with continued warming through gold color to red, to purple and finally to green, while the golden total color remains essentially unchanged. Samples are taken when each of the different colors is observed, and these samples are filtered, washed and dried and analyzed on iron. This analysis shows the following iron content:

% Fe

<td>Red reflex color</td><td> 8,9</td>

<td>Purple </td><td> 11,0</td>

<td>Green ”</td><td> 16,4</td>

These samples show, in addition to having the described, unusual color effects, marked improvements in lightfastness in comparison with the original, TiO₂-coated flakes.

Example XVI.

This example and Example XVIa illustrate the application of a nickel oxide layer to mica flakes that have been coated with TiOg in advance.

100 parts of silver-colored flakes A are added to a solution prepared by dissolving 200 parts of nickel chloride (NiC ^öH₂O) in 500 parts of sodium acetate (NaCgH₂O Og) in 2400 parts of water. The resulting slurry is heated to boiling and kept under boiling for about 4 hours until the flakes turn light green. The product is then filtered, washed chloride-free and dried at about 60 ° C. The dried material is light green with a sparkling silver appearance. Some of the dried flakes are calcined by heating to 950 ° C and the flakes are kept at this temperature for less than 30 minutes. The calcined product has a shiny yellow color with a sparkling golden reflex.

It contains 3.5 l of Ni. Dispersed in a vinyl composition (such as formulation D), a particularly attractive, gold-shimmering pearl-like effect is achieved.

Example XVIa.

An ammoniacal nickel chloride solution is prepared by dissolving 24 parts of nickel chloride (NiClg.OhgO) in 2000 parts of water and adding conc. ammonium hydroxide solution with constant stirring until a precipitate is formed, after which it dissolves. 100 parts silver colored flakes A (20.7 # TiO₂) is added, the slurry is heated to boiling and kept at boiling under reflux for about 4 hours. The slurry is then filtered, washed free of chlorides and dried to give light green colored flakes with silver reflex which show a noticeable improvement in light stability over untreated silver flakes.

Example XVII.

This example illustrates the application of a cobalt oxide layer to mica flakes previously coated with TiO₂·

100 parts of silver colored flakes A are added with stirring at room temperature to a solution prepared by dissolving 200 parts of cobalt chloride hexahydrate (CoC1₂· 6H₂0) and 300 parts sodium acetate in 2000 parts water. The resulting slurry is heated to boiling and kept for 1 hour under reflux. The slurry is then filtered hot and the press cake washed with water until it is chloride free. The cake is dried in an oven at about 80 ° C. The dried flakes give dispersed in cellulose acetate, as described in Preparation A, a dry film with a gray, metallic, pearl-like appearance. Calcination of the flakes for 1 hour at 950 ° C results in a light green product with silver reflex color. The product contains 2.9% Co.

Example XVIII.

This example illustrates the application of a copper oxide layer to mica flakes previously coated with TiO₂·

100 parts of silver-colored flakes A are added to an ammoniacal copper chloride solution prepared by dissolving 20 parts of copper chloride (CuCl₂) in 1000 parts of water, after which ammonium hydroxide (28% ΝΗ) has been added, until a precipitate is formed, after which it is again dissolved. The slurry is moderately heated at about 60 ° C for 1 hour to evaporate the ammonia and precipitate an aqueous copper oxide on the mica. The flake product is then isolated by filtration, washed free of dissolved salts and dried. The product consists of grayish flakes with silver reflex. Calcination of a portion of the product at 950 ° C for 15 minutes produces a darker, gray-black product, which retains the silver reflex and contains 2.4 $ Cu.

Example XIX.

Simultaneous precipitation with chromium oxide.

parts chromium sulphate (Cr₂(SO₂) 3.51 ^ 0) is dissolved in 1000 parts of water, to which are added 100 parts of water ground, white mica (CONCORD No. 200/325), and the slurry is well stirred to 90-100 ° C. 490 parts of titanyl sulfate concentrate (TiO₂-equivalent 14.4 ί - FA 80) is then added quickly, the slurry is heated again quickly to boiling and kept for about 3 hours under reflux firing. The product is filtered, washed free of soluble salts and tohka to give greenish flakes with a reddish gold reflex. When calcined at about 9 ° C, the product is transferred to yellow, pearl-like flakes with a luminous gold reflex. Coating compositions containing this pigment exhibit excellent light resistance.

Example XX.

Simultaneous precipitation with iron oxide.

100 parts in water ground mica (CONCORD No. 200/325) are slurried in 920 parts of titanyl sulfate solution (TiO₂equivalent 4,15 # FA 220), in which is dissolved 20 parts of anhydrous iron (III) sulfate. The slurry is thoroughly stirred and heated to 95 ° 100 ° C in about 30 minutes and kept at this temperature for about 4 hours. Samples of the slurry 'taken during the heating and diluted with water show on a black surface a progressive change in the color of suspended mica flakes. The final pigment is filtered, washed free of soluble salts and calcined for 1 hour at 900 ° C to give a yellow, pearl-like flake pigment, which gives a strong gold color in a coating composition. Such compositions exhibit a very high degree of light resistance.

Examples XXI and XXII.

The following examples illustrate the use of mixtures of the new pearl-like flake pigments and common colored pigments to achieve highly attractive decorative effects.

Example XXI. - Acrylic lacquer with mixtures of pigments.

These lacquers base? on a carrier mixture consisting of

85.4% mixed acrylic ester polymer (ACRYLOID A-101)

14.6 2 butyl benzyl phthalate (such as plasticizer portion) and a mixture consisting of:

$ monoacetate of ethylene glycol monoethyl ether% methyl ethyl ketone

1 »Toluene

An acrylic varnish of copper phthalocyanine blue (CPC) (produced in the usual manner in a ball mill) consists of:

3.2 parts copper phthalocyanine blue

66.2 parts carrier mixture

30.6 parts solvent mixture

The following blended varnishes are then prepared:

<td></td><td>A</td><td colspan="2">B</td>

<td>Silver flake pigments (Example Va)</td><td>4.75 parts</td><td colspan="2">4.75 parts</td>

<td>carrier mixture</td><td> 97,0</td><td> 97,0</td><td> 11</td>

<td>Paint of CPC blue</td><td> 7,8</td><td> 1,6</td><td>II</td>

<td>solvent Blend</td><td> 21,7 ”</td><td> 21,7</td><td> 11</td>

<td>The ingredients are mixed thoroughly</td><td>with stirring</td><td>with high</td><td>rapid</td>

hot for 15 minutes, diluted with additional solvent mixture to syringe consistency and sprayed with three double coatings on a suitable disc.

In lacquer A, the silver flakes / copper phthalocyanine blue ratio is 95/5 and the resulting slab exhibits a highly pleasing metallic effect with a more pronounced sparkle than is usually exhibited by lacquers containing aluminum flakes. up to as much as about 50:50.

In lacquer B, the ratio of silver flakes / copper phthalocyanine blue is 99/1 and the resulting slab shows the effect of a bluish-toned bead with a luminous rainbow shimmer under bright lighting.

Example XXII. - Alkyd varnish with a mixture of pigments.

A copper phthalocyanine green (CPC green) polychloro lacquer having the following composition is prepared by dispersion in a ball mill in the usual manner:

5.0 parts CPC green pigment

42.6 parts non-oxidizing coconut oil - modified alkyd resin solution (60% dry substance)

20.0 parts modified melamine formaldehyde resin ($ 55 dry substance)

16.2 parts of aromatic hydrocarbon solvent

16.2 parts of aliphatic hydrocarbon solvent.

Some of this varnish is blended with a pearl-like flake pigment as follows:

il

Golden flake pigments (Example Vb) 4.75 parts

CPC green lacquer 5.00 parts

Non-oxidized coconut oil - modified alkyd resin solution (60 55 dry substance) 58.4 parts.

These ingredients are mixed for 5 minutes by stirring at high speed, then 27.2 parts of modified melamine formaldehyde resin (55% dry substance) is added and stirring at high speed is continued for 5 minutes. The varnish is then diluted to spray consistency with a 50/50 blend of aromatic / aliphatic hydrocarbon or sprayed with triple coatings on a suitable board. This varnish contains a ratio of gold flakes / CPC green of 95/5 and the color is much yellower than for only CPC green varnish. The discs also show a shining gold sparkle.

EXAMPLE XXIII.15 200 parts of FeCl-2 (anhydrous) are dissolved in 2000 parts of water at room temperature, to which are added 40 parts of sodium acetate (NaCgH2Og) and 100 parts of wet ground muscovite mica, sold under the name CONCORD WET GROUND MICA Vr 200/325, which completely shines through gives a 200 mesh screen and about 90% through a 325 mesh screen and has an average diameter of the flake particles in the range of about 10 microns down to about 50 microns and an area of ​​about 3.2 m / g . The mixture is rapidly heated to 70 ° C with good stirring and kept at about 70 ° C for 1 hour. After heating for a few minutes, the mica flakes in the slurry assume the golden yellow appearance of the aqueous iron (III) oxide. When a sample of the slurry is diluted and observed against a black background, in addition to the overall golden-yellow appearance, a shiny colored sparkle appears as a reflex color from bluish silver at a brief warm-up to real silver at the end of the warm-up. This reflex color is an interference color that results from the deposition of the metal oxide film on the mica surface, whereby the film thickness and, consequently, the color varies with increasing heating time. After heating, the product is filtered, washed free of chloride ions and dried. It contains 18.1 55 iron (such as Fe₂And is a golden yellow powder which shows a brilliant sparkling cut to a thin film.

When dispersed in a typical coating composition, such as the alkyl lacquer preparation C, and applied to a metal plate, the resulting light-stable surface is golden yellow with a predominantly silver reflex. Considered under bright lighting at mirror angle, a brilliant game of rainbow shimmer also appears. When dispersed in an unburned vinyl film (such as in Preparation D), a brilliant golden colored pearl-like plastic composition is obtained.

It is clear that the amount of iron oxide deposited affects the interference color and can be varied by variations in the heating time or variations in the amount used.

Example XXIV.

The iron oxide coated flakes of Example 23 are calcined by heating in air at a temperature in the range of about 400-700 ° C, with the total color obtained ranging from brown at 400 ° C to pure at 600 - 700 ° C and a silver reflex color at all temperatures. As the calcination proceeds to higher temperatures, the interference10 decreases and largely disappears at temperatures above about 700 ° C. The product becomes a red pigment with no pearl-like properties at 950 ° C. Examination under microscope of uncalcined flakes and those calcined in lower temperature ranges shows a uniform layer of metal oxide particles which are extremely small and unclear in the oxalinated product. As the temperature increases, the particles develop distinct properties, but remain below about 0.1 microns in size until the temperature exceeds about 700 ° C.

Example XXV.

parts chromium sulphate (Cr₂(SO_in() +. 5H₂O) dissolved in 200 parts of water at room temperature and 100 parts of water-painted, white mica (average size 10 - 5.0 microns) are added. Powdered borax, (Na₂OllgOH₂O) is added slowly to the stirred slurry so that the pH of the slurry is maintained at about 5.0-5.5. Under these conditions, an aqueous chromium oxide is slowly precipitated and preferably deposited on the mica flakes. surface as a uniform, thin film, resulting in an interference color, which changes from gold to red to blue as the amount of precipitated, aqueous chromium oxide increases. Addition of small portions of borax is continued until all chromium sulphate is precipitated and the product is then filtered, washed free of sulphate ions and dried to give a light green powder (chromium such as Cr₂Oj) with a blue reflex color, when dispersed in a thin film, e.g. when rubbing between the fingers.

When used for the pigmentation of a cellulose acetate film, such as the preparation A, the light-resistant film has a light green color with a distinctive blue reflex. Examination of these flakes under electron microscope shows that the flakes are uniformly covered with the aqueous oxide film.

Calcination of these coated flakes in air at 700 ° C for 0.5 hours yields a green product of slightly less intensity but with a silver-blue interference color. The chromium oxide particles on the mica are less than 0.1 microns in diameter.

Example XXVI.

parts of vanadyl sulfate (VOSO 2 .2H₂O) dissolved in 1,600 parts of water at room temperature and 100 parts of wet ground, white mica (CONCORD WET GROUND MICA- # · 2OO / 325) added to the solution. Once the slurry is well stirred, powdered borax is added, (NagB ^ Oy.10H₂0) in small portions of sufficient rate to maintain pH in the range of 3.5 - 4.5, whereby vanadium tetra oxide is deposited on the mica flakes and a brownish gray color is obtained in overall appearance along with an interference color varying from silver to gold to red, when the amount of coating increases. The product is filtered, washed free of sulfate ions and dried to give brownish gray flakes. When these flakes are calcined in air at 300 - 400 ° C, they are transferred to light yellow flakes with an intense silver blue reflex color. These yellow flakes have a coating of about 15% vanadium pentoxide (V₂O, resulting from simultaneous calcination and oxidation of the aqueous tetraoxide. The vanadium pentoxide particles are less than about 0.1 micron in diameter. If the calcination temperature is significantly increased above 400 ° C, there is a marked tendency for particle growth and loss of pearl-like properties.

t

Particles, which are pigmented with these yellow flakes, show a brilliant yellow color with a silver-blue reflex. They are light-stable products.

The pigments described above offer the following remarkable advantages:

1st They can be produced and sold as dry pigments.

2nd These dry pigments show remarkable dispersion ease in compositions in which they are used.

· They show a pearl-like effect to such an extent that is not easily achieved with known pearl-like pigments.

4th They show a rainbow skimmer, many of which have a distinct, predominant hue, which can be varied as desired by simple changes in the compositions.

5th When properly stabilized, they offer a high degree of light fastness.

6th Most of them are chemically stable and they do not contribute to water stains on surfaces which are completed with compositions containing them.

7th They are heat stable and can be used in fire varnishes and in plastics, which are treated at high temperature.

Eighth They are completely non-bleeding in solvents and in common chemical agents to which the coating compositions may be exposed.

9th They are compatible with carriers for coating compositions and with plastic systems that usually meet.

10th They enable color effects that have not been achieved so far.