DE1467466B - Mother-of-pearl pigment and process for its manufacture - Google Patents

Description

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The invention relates to a mother-of-pearl-like pigment, written sandwich-like mother-of-pearl pigment is through consisting of mica, glass or plastic, a vacuum evaporation process is created that the platelets as a substrate and a water-insoluble installation of a relatively carefully selected metal sulfide coating with a high refractive index as a labored and costly installation needs. The Darperlmutt- and, if necessary, a color-producing composition of the applied titanium oxide or zirconium part. Oxydpigmente required a less complex Ausin the following description, if not armor, with the pigments by deposition otherwise stated, all parts and percentages are based on that of the solution. This procedure has Based on weight. however, the disadvantage that, for example, the titanium

»Mother-of-pearl-like pigments« are substances that calcine the io-dioxide coating at elevated temperatures

create a pearly sheen. The pigment particles must be in order to form a chemically stable film

are platelets that at least partially create from materials. The crystallization of the TiO ₃ coating

high refractive index. This pearling of the calcination led to the formation of very tiny ones

Pigments can be used as surface coatings, for example in the case of microscopic crystallites, which improve smoothness and

imitation pearls, are applied, or they affect the regularity of the coating. the

can be embedded in plastics. Pearlescent luster and the color intensity (if the coating

There is already a process for coloring pearls (the thickness of the interference film has) are considerable mother-like materials are known without their being less than with an ideal smooth coating. Lose pearlescent luster. The thicker the coating, the greater the quality-insoluble material Metal compound or an insoluble loss which so results.

Dye felled on the mother-of-pearl material. The sub- The patentee found that mother-of-pearl strat is suspended in organic solvent, the pigments can be created that the reagent forming the insoluble metal compound, zinc or other sulfides under atmospheric pressure zien, hydrogen sulfide or alkali sulfide as well as a can be deposited on substrate particles, Metal salt, are in alcoholic solution. For the 25 without any special equipment for vacuum precipitation a relatively short time, 10 to 20 minutes, evaporation process is required. Besides that needed. It is thereby achieved that the precipitation in the sulfide coating obtained in this way has a very similar one Time goes on in which the pigment is in moderate thickness and is even after heat treatments Form of individual particles precipitates. The precipitation should be free from errors. The strength of the zinc sulfide ended with this be before these particles produced pearlescent luster and color ink size over the colloidal 30 coating outgrow. A continuous metallurgy when the deposition in an interference film sulfide layer If there is no thick layer on the substrate particles, they are deposited with the previously known titanium deposits .... ^ ;. .. or zirconium oxide pigment coatings cannot be achieved.

The first pearlescent pigments, natural pearlescent substance, contained platelet-shaped crystals of 35 pigment with light-stable sulfide coatings of high guanine, which were obtained from fish scales and other fish refractive index on substrate particles, which were obtained from the tissue substance. The first synthetic - a stronger gloss and, in the case of interference-colored, mother-of-pearl-like pigments, consisted of basic objects, previously unattainable colors, such as lead carbonate, lead hydrogen phosphate, lead hydration. The pigment should also optionally be genarsenate or bismuth oxychloride, all of which are relatively luminescent. The object of the invention to have relatively high refractive indices and to be able to crystallize in platelets, in addition, to create a relatively single form. More recently, granular and economical processes for producing more complex types of pearlescent pigments have been developed. A pigment of this type is described in the German version of Extraordinary Uniformity in Lichtdurchlegeschrift 1 273 098. This pigment has non-stop and reflective properties,
consists of platelets in which a layer with a low- The object is achieved by a mother-of-pearl-like refractive index, ζ. B. magnesium fluoride, between pigment, consisting of mica, glass or artificial two layers with a high refractive index, ζ. B. fabric platelets as a substrate and a water-insoluble zinc sulfide, is layered. Another recently borrowed metal sulfide coating, which is characterized by intricate mother-of-pearl pigment, is characterized by the fact that the substrate particles consist essentially of titanium oxide or zirconium oxide coatings on a smooth surface and a size of three to four particles with a low refractive index. 100 μ have and that the substrate on both sides

If, as described below, the platelets have a metal sulphide coating made from a single layer of simple or complex mother-of-pearl pigments with an optical thickness Nd of 40 to a particular wall thickness range of 55 1000 ΐημ. According to a particular embodiment and the platelet thickness is sufficiently uniform, the substrate particles of the invention are mica, the mother-of-pearl pigments give the object, in platelets with a size between 5 and 50 μ. Preferably, or on which they are used, by means of light interference, these mica platelets have an essentially reference color and a pearl-like, even layer with a thickness of 200 to gloss. The color property is unusual, 60 600 ιτιμ, which has a crystalline structure. After a color is seen through reflected light and the grain - a further embodiment of the invention is a complementary color through the light that has passed through - the highly refractive layer of zinc sulfide is formed. This colored by interference pearl and is preferably luminescent,
mother pigments can therefore create a play of colors. In the production of a mother-of-pearl-like pigment that cannot be obtained with conventional color pigments, in which the 65 according to the invention becomes a water-insoluble metal color by absorption of a certain length of light wave sulfide on the platelet-shaped substrate particles. by mixing a suspension of the substrate particles

That is in the above-mentioned patent application with sulfide-containing solutions and a solution of a

Salt of metal precipitated; the particles are separated from the solution and dried. The process is characterized in that the metal sulfide is extracted from aqueous solution using an organic sulfur compound which releases sulfide ions in the pH range between 2.0 and 5.0 at a temperature between 60 ^° C. and the boiling point of the mixture within V ₄ to 5 Hours is deposited with stirring. Thioacetamide, thiourea, thioglycolic acid, thioacetic acid, thioformamide or thiosalicylic acid is used as the organic sulfur compound, and a zinc salt is preferably used as the water-soluble metal salt.

The above defined sulfide coated pigment particles can, after separation, preferably 1 to 4 hours at about 200 are heated to 1000 ⁰ C to produce the desired nacreous pigment.

The mother-of-pearl pigment produced according to the invention has an essentially uniform, defect-free one Sulphide coating which, when deposited in an interference film thickness, produces an extraordinary pearlescent luster and Has color intensities that are not achieved by the complicated mother-of-pearl pigments known to date became. In addition, the pearlescent layer is precipitated by the above-mentioned heating of the Sulphide coating converted into a form that has a significantly higher light stability than, for example the complex titanium or zirconia pigments discussed above.

It was further found that the sulfide-coated pearlescent pigments by a single Deposition of the sulfide coating can be generated in interference film thicknesses, the interference colors higher order and the unusual optical effects described below show. On the other hand, if such higher-order interference films using complex If mother-of-pearl pigments are to be produced from titanium dioxide, it is rather necessary with many coatings to work.

According to the invention, a mother-of-pearl pigment made from a zinc sulfide coating is preferably used. Zinc sulfide is essentially colorless and therefore gives the produced Pigment does not have its own absorption color. Furthermore, the color of such a pigment is in sulfide coatings in interference thickness can only be attributed to the interference effects, if not the pigment base has its own absorption color. In addition, a pigment containing zinc sulfide provides an excellent one Light stability and can optionally be made to be a luminescent mother-of-pearl pigment supplies.

However, it is possible to combine mother-of-pearl pigments according to the invention with other water-insoluble metal sulfides Manufacture by adding water-soluble salts or complexes of these metals with organic sulfur compounds implemented. The sulphides of cobalt, lead, mercury, manganese, cadmium, arsenic, antimony, For example, nickel, iron, copper, bismuth or tin can be used. When the sulfide coating Contains zinc sulfide, the colors produced by the coating are entirely sensitive to interference effects traced back. In the case of other sulfides, the colors are a combination of interference colors and inherent absorption colors of the sulphide in question. A SnS "cover, for example, of such a thickness that it has a has red interference reflection color, appears red with specular reflection and among other things when viewed Angle yellow. A NiS coating of a thickness producing a green reflection appears specular Reflection green and black at other angles. While the following description accordingly the preferred embodiment of the invention mainly deals with the formation of a Employing mother-of-pearl pigment from a zinc sulfide coating, the invention also includes the production of mother-of-pearl pigments other than water-insoluble metal sulfide coatings with a high refractive index include those described above.

The pigment particles provided with a thin sulfide coating have the properties of mother-of-pearl pigments and in the case of zinc sulfide show a blue or white reflection if the layer has a Has a thickness of about 20 to 60 ΐημ. If the thin film of zinc sulfide is a little thicker, the superimposed rays reflected from the opposing surfaces, so that a gain or quenching of the light of certain wavelengths and colored the pigment particles appear when illuminated with white light.

Interference cancellation of a given wavelength occurs when the reflections on the two film surfaces are completely out of phase. This occurs in the case of light incident perpendicularly on the film if λ applies for the wavelengths

Nd = (n- 1) λ / 2 ,

(D

whereby. N is the refractive index of the film, d is the film thickness, and η is a small integer such as 2, 3, and so on.

If the incident light is monochromatic and has wavelength λ , this well-known equation indicates that there is no reflection at all. On the other hand, when the film is illuminated with white light, all wavelengths except λ appear in the reflection.

The gain of a given wavelength occurs when the reflections off the two film surfaces are in phase with each other. In the case of light incident perpendicularly on the film, this occurs if

Nd = (2 η - [η = 1,2,3 ...}

is, where the letters have the meaning given above.

The index of refraction N for zinc sulfide is about 2.3. The thinnest film thickness that produces color by interference cancellation is that which removes the shortest wavelength of the visible spectrum, ie blue-violet, from the reflected light. If λ = 400 ΐημ is set for the light of this color, the film thickness necessary for this effect is about 87 ηιμ.

The reflected light produced has the complementary color (yellow in this example) to the color which was removed by reflection. Therefore, the thinnest film that can be removed by interference will have Color can produce a yellow reflective color. Have red, purple, blue, and green reflective films an increasing thickness.

Starting with purple, the reflection color becomes soft by removing a certain wavelength is increased by a gain color according to equation (2).

The approximate thicknesses of the zinc sulfide film used to create pearlescent pigments with different Interference colors are required are given in the following table:

Table I.
Optical thicknesses of the zinc sulfide-containing mother-of-pearl pigment

Reflection color

origin

Approximate optical
Thickness Nd (ηιμ) Approximate thickness
(πιμ) if N = 2.3 200 87 260 113 300 130 320 139 360 156 440 191 490 213 575 250 650 282

yellow

Fuchsin red
Purple ...

blue

Green ....
2. Yellow '..
2. Red ...
2. Blue ..
2. Green.

Excretion of blue-violet,
approximately 400 ΐημ

Elimination of green,
approximately 520 ηιμ

Elimination of yellow, 590 ηιμ
Reinforcement of purple, 400 πιμ

Excretion of orange, 610 ιημ
Reinforcement of blue, 480 ηιμ

Excretion of red, 650 πιμ
Reinforcement of green, 520 πιμ

Excretion of blue, 440 πιμ
Reinforcement of yellow, 590 πιμ

Excretion of blue-green, 490 πιμ
Reinforcement of red, 650 ΐημ

Elimination of yellow, 575 ΐημ
Reinforcement of blue, 460 πιμ

Excretion of red, 650 πιμ
Reinforcement of green, 520 πιμ

The designation »2. Yellow, 2nd red, "etc., describes the second occurrence of each color with increasing thickness and is preferred to the terms" second-order yellow "etc. The usual definition of the higher-order interference colors by the atomic number is not always in agreement with the value "n" in the above interference equations (1) and (2), where η sometimes also refers to the order. The nomenclature given above has therefore been used here.

Further increases in the thickness of the zinc sulphide layer over those indicated for the second green reflection Value creates third reflection colors. The interference film for the third green is approximate optical thickness of 1000 ΐημ. Interference films with greater optical thicknesses do not have the Color intensity of the second and third colors, so that their production is relatively uneconomical.

The interference colors created in this way depend on the angle of observation (the colors in Table I are those at normal incidence), whereby the colors correspond to the wavelengths, the thinner films correspond, move when the angle of incidence increases, d. H. the direction of the incident light moves away from the normal to the surface. The first reflection colors show a moderate shift the wavelength when the angle of observation changes. Hence green goes blue, blue goes purple, Fuchsin red in orange and gold in a pale yellow tone. The second colors, on the other hand, show you much further change in the reflected wavelength, the second green changing with increasing angle of incidence in blue and then purple that changes

second blue in purple and then in red, the second red in green gold and the second gold in blue green. Through Coating dark curved surfaces with such mother-of-pearl pigments that make these surfaces higher Issue interference colors, can obviously

remarkable iridescent effects can be achieved. You get similar effects when you use the Pigments of the second interference are embedded in plastics, with the pigment particles in uneven patterns are aligned.

These pearlescent pigments are made by using zinc or another sulfide an aqueous solution using an organic sulfur compound as a sulfide source will. In comparative tests, the patent

Proprietor found that the conventional method of forming zinc sulfide by blowing H ₂ S-GaS into a zinc salt solution as a method of coating the substrate particles used therein is highly unsatisfactory. The precipitation of zinc sulfide with

H ₂ S only creates discrete ZnS particles that have little or no tendency to coat or adhere to the particulate matter present. It has been found, however, that a smooth, adhesive ZnS film can be deposited if the sulfide

source an organic sulfur compound that releases sulfide ions, such as thioacetamide, thiourea, thioglycolic acid, Thioacetic acid, thioformamide or thiosalicylic acid.

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The source of zinc in the reaction is one in water considerably higher than the stability of one not through rigem medium soluble zinc compound in about 0.25 heat treated complexes given above up to 7.5%, preferably 0.5 to 3.5% solution, mother-of-pearl pigments made from titanium dioxide, which is very chalky, calculated as ZnO. Suitable soluble salts are zinc. However, it is desirable that the sulfide-coated pig-

acetate, zinc chloride, zinc sulfate, zinc formate and zinc 5 ment after drying in air or an inert nitrate. Heat treatment atmosphere at temperatures

The concentration of the sulfur compound depends between 200 and 1000 ° C. In general, it depends on the zinc concentration. A higher temperature of the specified range equimolar ratio of sulfur to zinc is followed by the treatment preferably in nitrogen or desirable. Satisfactory results have also been obtained from another non-oxidizing gas, e.g. B. helium, using about 0.5 molar ratios of argon, carbon dioxide, etc.
achieved up to 3 moles of sulfur per mole of zinc. It was found that the heat treatment the

The substrate particles on which, according to the invention, the density of the sulfide coating increases, as a result of which the coating of zinc or other sulfide particles is deposited refractive index and thus the reflectivity, have the shape of substantially increases, and the film thickness and accordingly the bestowed smooth platelets with a predominant size shift of the interference colors is reduced. Flakes coated with from about 5 to 50 microns and a thickness of about zinc sulfide will retain 50 to 2000 millimicrons. The treatment preferably consists of their smooth surfaces, while pigments coated with substrate material made of mica flakes, expediently titanium dioxide, for example in the case of usually those made of muscovite. However, other types of mica of the heat-treated shrink flakes can also be used if they become somewhat rougher. This roughening verrinso z. B. biotite, plogopite, vermiculite and various gert the reflective reflection and increases the synthetic mica, especially the natural light scattering. The avoidance of light scattering resemble borrowed white mica. The mica particles of the coated platelets are of particular concern are preferably "water-milled" and have a thickness for coatings of interference thickness, since they are smooth, between the sieve openings 0.037 and areas that do not cause this scattering, maxi-0.105 mm. The surfaces were created according to the paint intensity. The heating determined with the BET method to about 2 to 6 m ^a / g. Particularly sulfide coated pigment at temperatures of the same good results were achieved using about 200 ⁰ C or higher increases the light stability beFractions that went through sieves with 0.105, 0.044 30 without affecting the smoothness of the coating surface or 0.037 mm opening of the sieve and is influenced,
which were practically free of fine particles. It has been found that at treatment temperatures

Though preferably of mica as temperatures of about 700 ⁰ C or above the amorphore pigment substrate can be used erfmdungs- zinc sulfide coating may also include other particulate materials is converted to the top 35 according to the crystalline form (sphalerite). This increase in crystallinity specified sizes can be used. Therefore, this unexpectedly increases the light stability and pearlescent pigment can also be indexed by deposition of the sulphide - produces a considerable increase in the refractive coating on flakes made of glass, plastic, etc. and the reflectivity of the pigment surface. without affecting its smoothness.

The acidity of the reaction mixture is determined according to 40

the particular organic T? used as a sulphide source? 'q' 1 1

Connection terminated. If thioacetamide is used ^e "

the reaction takes place in an acidic solution, pre- White pearl pigment

preferably in the pH range from about 2.0 to 5.0,

expediently between 3.5 and 4.5. The solution 45 40 parts by weight of zinc acetate dihydrate and 14 Gekann to the desired pH range, for example, parts by weight of thioacetamide in 890 parts of water with formic acid, hydrochloric acid, sulfur- dissolved. 48 parts of mica acid are added to this solution or nitric acid. added leaves (water-milled muscovite with

For the separation, the aqueous mixture, which is a specific determined by the BET method, the zinc salt, the organic sulfur compound and 50 surface area of 4 m ² / g).

Contains the substrate particles for about ₄ to 5 hours. The suspension is mixed with 43 parts of formic acid

elevated temperatures between about 6O ⁰ C and brought to pH 4.0. The reaction mixture heated to the boiling point of the aqueous system. It is then heated to the boil and refluxed for 90 minutes within the specified ranges, the mica having longer reaction times if the reaction was kept in suspension. Thereafter, the mixture is heated to low temperatures. The mica coated with zinc sulphide was removed. The mica or the other substrate is in this case in trated, washed with water and dried at 110 ° C., the suspension is kept; the zinc deposited on it, a pearlescent white product, sulphide coating is essentially in amorphous form. Microscopic examination by means of reflected

and produced the desired pearlescent pig- 60 light at 1000 times magnification showed a smooth ment. even zinc sulfide layer on the mica

The pigment particles are then separated off and flake.

for example, ^{dried at about 110 °} C. and preferred The light stability of the pigment produced was

wise a heat treatment at temperatures between determined by using pigment samples are subjected to ^{about 200 and 1000 0 C.} The light 65 of a drawing spatula in a nitrocellulose lacquer is stability of the sulfide-coated pigment, embeds the on and then to a UV-resistance tester 110 ⁰ C dried, but not a downstream (fade-0-Meter) were used. The coating was subjected to the following heat treatment, was composed of 4% coated flakes in a clear,

non-stabilized nitrocellulose varnish of the following composition:

Nitrocellulose 15/20 seconds *) ... 3.0%

Nitrocellulose 30/40 seconds *) ... 6.5%

Ethanol 5.1%

n-butyl acetate 85.4%

100.0%

*) Measured according to the falling ball method using a comparison solution consisting of 12.2% nitrocellulose in a mixture of 25% denatured ethanol, 20% ethyl acetate and 55% toluene.

After 55 hours the nitrocellulose film had turned pale brown.

Example 2
Light stabilized pearl pigment

The dry leaflets produced according to Example 1 were heated ^{to 300 ° C. in air for 1 hour.} The light stability of the heated pigment was measured by preparing a 4% suspension of the coated mica flakes in nitrocellulose and drawing the suspension (using the "draw-down technique") into a film and testing it as in Example 1 for light stability. The light stability was increased to 85 hours compared to 55 hours for the pigment produced according to Example 1.

Example 3

Light stabilized pearl pigment
Another sample of the dry pigment produced according to Example 1 was ^{heated to 700 °} C. for 1 hour in nitrogen and tested for light stability using the technique described above. The light stability was increased to over 100 hours.

Examples 4-11
Interference colored pigments

The procedure of Example 1 was repeated, except that the ratio of mica to zinc salt was used was reduced to give thicker zinc sulfide coatings that produce color through light interference. Several pigment samples were made by adding zinc acetate dihydrate and thioacetamide in 890 parts Water were reacted, with enough formic acid in each case to adjust the acidity at pH = 4 was used.

The proportions of reactants used (in percent by weight) to make pigments with different interference colors are given in the following table:

Table II
Interference-colored zinc sulfide mica pigments

A. Applied ratios of mica ZnC ₂ H ₃ O ₃ • 2H ₂ O Reaction partner Ants
acid at
game 35.5 48.0 Thioacet
amide 51.6 4th 33.2 49.7 16.5 53.5 5 26.2 55.9 17.1 60.0 6th 22.5 57.7 19.2 62.0 7th 21.2 58.7 19.8 62.2 8th 20.0 60.0 20.2 64.5 9 16.0 61.8 20.6 66.5 10 14.0 63.7 21.2 68.5 11th 21.8

B. Property of the pigments produced Thickness for N = 2.1 at
game Reflection
color Nd an
approached approximately 95 ηιμ ⁵ 4 gold 200m [e.g. approximately 124 πιμ 5 Fuchsin red 260 ηιμ approximately 152 ΐημ 6th blue 320 ηιμ approximately 171 πιμ 7th green 360 ηιμ approximately 210 ΐημ ! O ⁸ 2. Gold 440 ηιμ approximately 233 πιμ 9 2. Red 490 ΐημ approximately 274 ηιμ 10 2. Blue 575 πιμ approximately 310 πιμ 11th 2. Green 650 πιμ

The colors indicated were those of the coated ones

Leaflets when viewed against a black background.

The pigment products were ^{heated to 500 °} C. for 60 minutes. The heat treatment gave the pigments a considerably increased light stability and did not cause any significant change in their colors. The examination of all the pigments produced by reflection microscopy at 1000 times magnification showed that all the coatings formed in this way were smooth and uniform and that even after the heat treatment to improve the light

Stability remained that way.

A further heat treatment at 700 ^° C. in nitrogen caused a color shift to the color that corresponds to a somewhat thinner film. The coatings stayed smooth and even as they went through

Reflection microscopy at 1000X magnification.

Example 12

Multiple interference colored pigments made in a single deposit

Since the nacreous zinc sulfide coatings build up on the substrate particles in a regular manner, different types of pigments can be produced in the course of a single sulfide deposition by periodically peeling off pigment samples before the test is complete. For this purpose, the reactants of Example 11 are used in the precipitation process of Example 1, with uniform proportions of the product being withdrawn after various time intervals. The leaflets were ^{dried at 110 °} C., suspended in nitrocellulose lacquer and then drawn out to form a film. The reflection color of the respective film is given in the following table:

Table III

Pigment samples generated during a single ZnS deposition

Time after reaching the boiling point Reflection color 35 minutes "White"
gold 60 42 minutes Red
violet 45 minutes blue
green 47 minutes 2. Gold 50 minutes 2. Red
2. Blue
2. Green 54 minutes 65 56 minutes 60 minutes 65 minutes 76 minutes

Example 13
Luminescent mother-of-pearl pigments

500 parts of the dry product prepared by the method of Example 1 are mixed _{with 2 parts of NaCl and 0.0211 parts of CuCl 2.} The mixture is heated to 850 ° C. in about 1 hour and then left to cool in air. Finally, the product was _{washed with H a} S-saturated water.

The resulting phosphor luminescent when irradiated with UV light having a wavelength of 3650 Å Green with a moderate green sheen. The high reflectivity of the product increased the Fluorescence intensity above that observed with ordinary luminescent zinc sulfide will.

In the case of other activators instead of the copper salt given above, other luminescent properties can be used be achieved. Thus, the use of a manganese salt activator gives an orange luminescent product, and a silver salt activator for example, gives the pigment a blue luminescence.

Example 14
White pearl pigment on glass flakes

30th

The procedure of Example 1 was repeated with the difference that the amount of water doubled and the 48 parts of mica were replaced by 290 parts of glass flakes with an average thickness of 1 to 2 μ became. The coating reflected white light.

The product was first dried at 110 ° C. and then heated as in Example 2.

After embedding in a polyester resin plate, the coated flakes showed an effective light reflection, and they could be used to make light polarizer plates. The originals uncoated flakes were due to the low degree of reflection of glass in polyester ineffective because the two substances have almost the same refractive indices.

50 Example 15

Pigment from SnS _a coating on mica flakes

31.9 parts of stannous chloride pentahydrate and 14 parts of thioacetamide are dissolved in 800 parts of water. 48 parts of mica flakes are added to the solution. The suspension had a pH of about 0.5.

The reaction mixture was heated to boiling with stirring and refluxed for 2 hours. The tin (IV) sulfide-coated mica was filtered off, washed with water and ^{dried at HO 0} C, giving a shiny gold product.

Microscopic examination with reflected light showed a smooth, uniform appearance on the mica flakes Tin (IV) sulfide coating.

Example 16

SnS _a -coated mica pigment
with red reflection color

The procedure of Example 15 was repeated except that the amount of mica flakes was reduced to 24 parts. After drying at 100 ⁰ C and embedding in a nitrocellulose film, the SnS generated a red color _a -überzogenen mica flakes when they were at specular reflection, that is, checked at right angles, and a yellow color when viewed at different angles.

Example 17
Pigment made from CdS-coated mica

33.3 parts of cadmium chloride and 14 parts of thioacetamide were dissolved in 800 parts of water. To the 48 parts of mica flakes were added to the solution. The suspension was made up with hydrochloric acid pH = 3.0 brought.

The reaction mixture was then heated to boiling temperature with stirring and refluxed for 90 minutes. The mica coated with cadmium sulfide was then filtered off, washed with water and ^{dried at HO 0} C, giving a product with a gold-pearl shine.

Microscopic examination by reflected light showed a smooth, uniform coating of cadmium sulfide on the mica flakes.

Claims (5)

Patent claims: 1. Mother-of-pearl-like pigment, consisting of mica, glass or plastic flakes as the substrate and a water-insoluble metal sulfide coating, characterized in that the substrate particles have a substantially smooth surface and a size of 3 to 100 microns and that the substrate has a metal sulfide coating on both sides each from a single continuous layer with an optical thickness (Nd) of 40 to 1000 πιμ carries. 2. mother-of-pearl-like pigment according to claim 1, characterized in that the substrate particles Mica platelets are between 5 and 50 μ in size. 3. mother-of-pearl-like pigment according to claim 2, characterized in that the mica flakes wear a substantially uniform layer with a thickness of 200 to 650 πιμ, which a possesses crystalline structure. 4. mother-of-pearl-like pigment according to claim 3, characterized in that the highly refractive Layer of zinc sulfide is formed and is preferably luminescent. 5. A method for producing a mother-of-pearl pigment according to claims 1 to 4, at which a water-insoluble metal sulfide on the platelet-shaped substrate particles by mixing a suspension of the substrate particles with sulfide-containing solutions and a solution of a Salt of the metal is precipitated, the particles are separated from the solution and dried, thereby characterized in that the metal sulfide from aqueous solution using an organic, Sulfur compound releasing sulfide ions is deposited in the pH range between 2.0 and 5.0 at a temperature between 6O ⁰ C and the boiling point of the mixture within V ₄ to 5 hours with stirring.
6. The method according to claim 5, characterized draws that the organic sulfur compound thioacetamide, thiourea, thioglycolic acid, Thioacetic acid, thioformamide or thiosalicylic acid and, as the water-soluble metal salt, a zinc salt is used.