JPH07157687A - Production of bluish brilliant white nacreous pigment - Google Patents

Abstract

PURPOSE:To obtain a brilliant white nacreous reduced in the yellowness incidental to conventional white nacreous pigments and having a bluish and clean hue. CONSTITUTION:This production method the title process comprises suspending a white nacreous pigment, prepared by coating mica flakes with titanium dioxide, in an aqueous medium and precipitating cobalt-aluminum oxides from a cobalt-aluminum salt on the surface of the pigment, and a precipitant which forms ammonia upon heating is used as the precipitant for the cobalt-aluminum salts.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a pearlescent pigment, and more specifically to a field of resins, paints, inks, building materials, etc., which has an unprecedented bluish tint and a clean color tone. In addition to the above, it is an object of the present invention to provide a bluish white pearlescent pigment which is useful in a coloring field where design is required.

[0002]

BACKGROUND OF THE INVENTION Conventionally known white pearlescent pigments are
Flake-like mica or a similar product is coated with titanium dioxide to give a white pearlescent pigment. The pearlescent luster of pearlescent pigments is better for substances with higher concealing properties, and part of the scattered light interferes with the light when passing through the titanium dioxide layer, and the stronger light exerts the luster. . Titanium dioxide is currently considered to be the most effective of its effects. However, the conventional bright white pearlescent pigment has the excellent properties as described above, but on the other hand, the hue is not pure white but has a yellowish hue, and as a result, the article colored with the pigment has brightness. In many cases, the image of being dirty is received, and it is desired to eliminate the yellow color tone as a market request.

[0003]

Problems to be Solved by the Invention The color tone of the yellowed white pearlescent pigment as described above is often perceived to be image-wise, and there is an urgent need to improve this point. As a method of solving such a problem, in general paint systems, there is a method of mixing a small amount of blue pigment into the paint, which is called bluing. Incorporation into the white pearlescent pigment results in impairing the excellent luster of the white pearlescent pigment.
Therefore, the object of the present invention is to meet the above-mentioned demands of the prior art,
Conventional white pearlescent pigments have little yellowing, have a bluish and clean color tone, and are useful in fields such as resins, paints, inks, and building materials, as well as in coloring fields where design is required. It is to provide a white pearlescent pigment.

[0004]

The above object can be achieved by the present invention described below. That is, the present invention involves suspending a white pearlescent pigment obtained by coating mica flakes with titanium dioxide in an aqueous medium, and depositing cobalt-aluminum oxide from cobalt-aluminium salt on the surface of the pigment, cobalt. And a precipitant which produces ammonia upon heating, as a precipitant for aluminum salts, and a method for producing a bluish white pearlescent pigment.

[0005]

In the present invention, the titanium layer surface of the white pearlescent pigment obtained by coating mica flakes with titanium dioxide,
A yellow substance disappears by coating with a substance that is uniform and smooth and develops a blue color. At that time, the coating material is required to be transparent so as not to interfere with the interference of light, and is required to have an affinity with the titanium dioxide layer as the base. Considering the above points,
By providing a cobalt-aluminum oxide coating layer containing cobalt oxide and aluminum oxide as a main component, which has the highest transparency as an inorganic pigment as a coating material on the titanium dioxide layer and has a good affinity with titanium, yellowing To provide a bluish bright white pearlescent pigment that has a low bluish and clean color tone and is useful in the fields of resins, paints, inks, building materials, etc., as well as in the coloring field where design is required. Can be done.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail with reference to the preferred embodiments. As the mica flakes that are the coating matrix of the bright white pearlescent pigment of the present invention, commonly used muscovite flakes are preferred, but the coating matrix that can be used is limited to these muscovite flakes. Of course, if the surface smoothness and aspect ratio are similar to those of muscovite flakes, it goes without saying that other mica flakes can be used as well.

The particle size of the mica flakes is 1 to 100 μm.
The grade is used, but is preferably 20 to 50 μm.
Those having a relatively uniform particle size and a thin thickness of about 0.1 μm are particularly preferable. The titanium dioxide used for coating the mica flakes uses a titanium salt as a titanium source, and more specifically, a reagent such as titanyl sulfate or titanium tetrachloride or an industrial material can be used. As the cobalt-aluminum oxide coating the surface of the titanium layer, corresponding reagents or industrial cobalt or aluminum salts can be used as these metal sources.

As a method for coating the titanium dioxide on the mica flakes, a preheated mica flake suspension is prepared.
This is a method of depositing a hydrate or an oxide of titanium on the mica flakes by adding a previously dissolved titanium solution and hydrolyzing the titanium salt, and this method is known per se. The titanium dioxide-coated mica flake slurry thus obtained can be washed with water, and the resulting slurry can be directly subjected to coating with cobalt-aluminum oxide for bluing. At this time, the slurry is once filtered, the obtained cake is dried at 120 ° C. for about 12 hours, and then the dried flakes are dried at 700 to 900.
It is also possible to subject it to a coating with cobalt-aluminum oxide after heat-treating it at a temperature of about 1 hour.

The titanium dioxide-coated white mica flakes obtained as described above exhibit excellent brilliance regardless of whether they are heat-treated or not, but they have a slight yellowish color tone. , There is still the problem of having a dirty image. In order to provide the titanium dioxide-coated white mica flakes with a bluish clean color tone, it is necessary to further coat the smooth surface of the flakes with a substance that develops blue color. As a result of the investigation, it was found that cobalt blue pigment containing cobalt-aluminum oxide as a main component is most suitable as a coating material.

That is, unlike titanium dioxide, the substance to be coated on the titanium dioxide-coated mica flakes needs to have transparency, and for that purpose, they are very fine particles.
A transparent substance without hiding property is desired. At the same time, it must have a good affinity with titanium dioxide. Furthermore, in the case of the present invention, it is necessary during the coating process for the titanium dioxide coated mica flakes that cobalt-aluminum oxide or a precursor thereof is extruded onto the titanium dioxide coating of the mica flakes. It is preferable to synthesize the pearlescent pigment (1) by a wet method.

In consideration of the above points, when a substance which develops blue color as a coating material is examined, a blue dye other than the cobalt-aluminum oxide pigment (cobalt blue pigment),
Although there are cyanine blue, ultramarine, etc., the dye is extremely inferior in terms of durability, and in the case of phthalocyanine blue, it has a poor affinity with titanium dioxide when viewed as a coating material, and the ultramarine is very reddish and very beautiful. Although the color tone is blue, it is difficult to synthesize by the wet method. For the above reasons, cobalt-aluminum oxide containing cobalt-aluminum oxide as the main component was selected as the most suitable coating material in the present invention.

The method for coating titanium dioxide-coated mica flakes with cobalt-aluminum oxide will be described below step by step. In the suspension of the bright white mica flakes previously coated with titanium dioxide, cobalt-aluminum oxide main component cobalt and aluminum salts and a substance that generates ammonia by heating as a precipitant, preferably urea or its The derivative is dissolved and a suspension is prepared.

Next, this solution is heated to 70 to 100 ° C. and kept constant. This heating causes urea or its derivative to begin to hydrolyze, producing ammonia as a precipitant for the metal salt,
Cobalt and aluminum oxides or hydrates thereof are projected into uniform and fine particles, and since this precipitate is easily adapted to the titanium dioxide layer, it gradually deposits on the titanium dioxide layer of titanium dioxide-coated mica flakes. . In this way, the reaction is carried out for a certain period of time, and when the pH rises to 7 or higher, preferably to 8, the coating reaction is terminated. After the reaction, the slurry is washed with water and filtered, and the obtained cake is dried at 120 ° C. for about 12 hours. Then 700 to 1,1 in an oxidizing atmosphere
Heat treatment is performed at 00 ° C. for 0.5 to 2 hours.

The cobalt of the present invention thus obtained
The bright white mica flake pigment coated with aluminum oxide is a bright white pearlescent pigment having a more improved brightness than that of the pigment before coating and a reduced yellowing and a bluish pure white.

The cobalt and aluminum salts used for the coating include the sulfates, nitrates, chlorides, acetates and the like of cobalt and aluminum which have been conventionally used for producing cobalt-aluminum oxide pigments. In consideration of bluing, the cobalt-aluminum oxide pigment does not need to contain a large amount of cobalt, which can be used and is used in consideration of bluing. Considering the characteristic called transparency required for the present invention, it is more effective that the content of the colorless and transparent aluminum oxide is large. Therefore, the compounding ratio of cobalt-aluminum is cobalt / aluminum =
It is 0.1-0.5: 2.

Although the coating ratio of cobalt-aluminum oxide to titanium dioxide changes depending on the above-mentioned mixing ratio of cobalt and aluminum, it is 50% by weight or less of titanium dioxide, preferably 1 to 50% by weight. It is good. If the coating material is too much, peeling or cracking from the titanium layer surface of the cobalt-aluminum oxide occurs,
As a result, the surface of the flake is roughened and the smoothness of the flake is lost, resulting in impairing the luster of the finally obtained pearlescent pigment. On the other hand, if the amount is too small, the resulting pigment remains yellowish.

In the method for producing a pigment of the present invention, such a metal salt of cobalt and aluminum is introduced into a suspension of bright white mica flakes coated with titanium dioxide. Concentration of suspension is 10
It is preferably 0 g / liter or less. If the concentration is too high, agglomeration of mica flakes will occur during the coating reaction, resulting in a marked loss of glitter.

In the present invention, it is preferable to use urea or a derivative thereof as a precipitant which causes the metal salt as an oxide or a hydrate thereof to be projected on the surface of the mica flakes.
By dissolving urea or its derivative in the above mica flake suspension and adding the above metal salt, no change occurs at around room temperature, but when heated with stirring, it is uniformly dissolved in the entire mixing system. The urea or its derivative starts to decompose to generate ammonia, and uniform and fine cobalt-aluminum oxide particles are projected on the titanium dioxide layer of the mica flakes. The reason for this is that urea or its derivative, which is a precipitating agent, has no local concentration gradient in the treatment liquid, and it cannot be obtained by the method of successively dropping the precipitating agent by the conventionally used dropping method. Coating of the mica flakes with cobalt-aluminum oxide with perfect uniformity is guaranteed.

The above-mentioned urea or its derivative as a precipitating agent is a metal 1 to cobalt and aluminum metal salt.
The use of 1 to 5 mol per equivalent is preferred. If the amount is more than this range, the cobalt-aluminum oxide coating film to be coated will be cracked, the surface will be roughened, and mica particles will be aggregated.

Thus, the mixed suspension of the glittering white mica flakes, the metal salt and urea or its derivative is heated and stirred at a temperature range of preferably 70 to 100 ° C. for 0.5 to 12 hours, Deposition of cobalt-aluminum oxide is carried out on the titanium dioxide layer of the mica flakes.

Next, the flake slurry on which the metal oxide or its hydrate is deposited is washed with water and filtered, and the flake slurry is dried at 120 ° C. for 1 hour.
It is dried for about 2 hours, and the dried coated mica flakes are heat-treated in an oxidizing atmosphere at 700 to 1,100 ° C. for 0.5 to 2 hours to obtain the bluish and bright white pearlescent pigment of the present invention. You can get it. The pearlescent pigment of the present invention thus obtained has a significantly improved luster compared with a product not coated with cobalt-aluminum, and has a color tone close to pure white with a bluish tinge with little yellowing.

[0022]

EXAMPLES Next, the present invention will be specifically described with reference to Examples and Comparative Examples. The parts or% in the text are based on weight unless otherwise specified. Example 1 80 parts of the bright white mica flakes of Comparative Example 1 below were suspended in 1,000 parts of water, and then 1.5 parts of cobalt nitrate hexahydrate, 18.8 parts of aluminum nitrate 9-hydrate and 25 urea. Take part and add to the above suspension. This mixed suspension is well stirred to uniformly dissolve each component, and then the temperature is started to rise, and when the temperature reaches 100 ° C., the temperature is kept constant and the state is maintained.

After a while, precipitation of hydrates of the respective metal oxides starts to appear on the titanium-coated mica flakes, but after that, heating and stirring are continued, and after 2 hours, the reaction is terminated, washed with water and filtered . 120 cakes obtained
Dry at ℃ for 12 hours or more. The dried mica flakes were heat-treated at 900 ° C. for 1 hour in an oxidizing atmosphere to obtain a bluish bright white pearlescent pigment of the present invention. This product was made into a paint with an acrylic cracker and applied with art paper with a 6 mil film applicator. It was brighter than the pearlescent pigments of Comparative Examples 1 and 2 below, and was pure white with less aggregation and yellowing of particles. A coating film having a color tone close to that of the above was obtained.

COMPARATIVE EXAMPLE 1 550 parts of water was added to 58 parts of scaly muscovite flakes having a thickness of 0.05 to 0.2 μm and an average particle size of 40 μm, and the mixture was suspended with stirring to prepare a solution A. Next, titanyl sulfate 7
Mix 0 parts (titanium dioxide 32%) with 150 parts water,
Titanium was dissolved, and 100 parts of 98% sulfuric acid was added to prepare a solution B. The solution A was heated with stirring, and when the temperature reached 95 ° C., the solution B was charged and aged for 3 hours, and then the produced dioxide-coated mica flake slurry was washed with water and filtered to obtain a filter cake at 120 ° C. It was dried for 12 hours.

The dried cake is then placed in an oxidizing atmosphere for 8 hours.
It was heat-treated at 00 ° C. for 1 hour to obtain bright white mica flakes coated with titanium dioxide. When this product was made into a paint with an acrylic cracker and applied with art paper with a 6 mil film applicator, the film had a color tone close to white with glitter but a yellowish color tone as a whole.

Comparative Example 2 Bright white mica flakes 80 produced according to Comparative Example 1.
Parts are suspended in 100 parts of water, and then 1.5 parts of cobalt nitrate hexahydrate and 18.8 parts of aluminum nitrate nonahydrate are added.
Dissolve in 00 parts of water and use caustic soda as a precipitant solution.
4 parts are dissolved in 100 parts water. The metal salt solution and the caustic soda solution thus obtained were gradually dropped simultaneously at PH8 into the stirring mica flake suspension solution to give a hydrate of the metal oxide on the bright white mica flake. Let it break out. After completion of the dropping, the coated mica flakes are washed with water and filtered, and the obtained cake is dried at 120 ° C. for 12 hours or more.

The hydrate-coated mica flakes of metal oxide were already highly agglomerated at this point, and the glittering effect seen before the addition of the metal salt was almost lost. The dried mica flakes were heat-treated in an oxidizing atmosphere at 900 ° C. for 1 hour to obtain the target bluish bright white pearlescent pigment. When this product was made into a paint with an acrylic cracker and applied with art paper with a 6 mil film applicator, a blue color was exhibited, but no glittering property was observed. or,
The aggregated mica flake particles were in a state of coarse particles in the paint without loosening.

[0028]

[Effects] According to the present invention as described above, an inorganic pigment as a coating material has the highest transparency and has an affinity with titanium dioxide on the surface of a titanium layer in a white pearlescent pigment obtained by coating mica flakes with titanium dioxide. By providing a good cobalt-aluminum oxide coating layer, it has a bluish and clean color tone with less yellowing than ever before, and it has a good design in addition to fields such as resins, paints, inks and building materials. A pearlescent pigment useful for the required coloring field is provided.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mineki Matori 1-7-6 Nihonbashi-Bakurocho, Chuo-ku, Tokyo Dainichi Seika Kogyo Co., Ltd.

Claims (5)

[Claims] 1. A white pearlescent pigment obtained by coating mica flakes with titanium dioxide is suspended in an aqueous medium, and cobalt and aluminum oxide are deposited from a cobalt-aluminum salt on the surface of the pigment. A method for producing a bluish bright white pearlescent pigment, which comprises using a precipitant that produces ammonia when heated as a precipitant for an aluminum salt. 2. The method for producing a bluish white pearlescent pigment according to claim 1, wherein the precipitant is urea or a derivative thereof. 3. The amount of urea or its derivative used is metal 1
The method for producing a bluish bright white pearlescent pigment according to claim 1, wherein the amount is in the range of 1 to 5 mol per equivalent. 4. The method for producing a bluish white pearlescent pigment according to claim 1, wherein the titanium dioxide-coated mica flakes are used at a slurry concentration of 100 g / liter or less. 5. The method for producing a bluish white pearlescent pigment according to claim 1, wherein the coating is heat-treated at 700 to 1,100 ° C.