JPH0428031B2 - - Google Patents

Description

[Detailed description of the invention]

"Industrial Application Field" The present invention is a new scale technology in which a hematite particle layer is formed on the surface of inorganic particles (hereinafter referred to as silica particles) containing at least 15% by weight of _SiO2 as a core. This invention relates to a red composite pigment and its manufacturing method. ``Conventional technology'' Hematite, also known as red iron, is a natural,
Both synthesized particles are red to brown in color. It has long been widely used as a light-fast, stable, and non-toxic red pigment. Many manufacturing methods are known, and the ones obtained by the known methods are granular powders, but spherical, plate-shaped, needle-shaped, and disc-shaped powders can also be produced. The optimum particle size of red pigment (hematite) as a red pigment is in the range of 0.1 to 0.6 μm. When the size is larger than this, the dispersibility improves, but the brightness gradually decreases to orange-red, reddish-brown, purple-red, and purple-black. When the particle size is around 1 μm, the color becomes purple-black, making it unsuitable as a red pigment. The relationship between the particle size and color of these pigments is detailed by Nobuoka in Color Materials 55 [10] 758 (1982). Optimum particle size for red pigment
Since particles of 0.1 to 06 μm are fine, they have a large amount of oil absorption and have strong agglomeration, so they have a major drawback of poor dispersibility. If the particle size is 1 μm or more, which has good dispersibility, the color becomes purple-black and is unsuitable as a pigment. "Problems to be Solved by the Invention" The purpose of the present invention is to maintain the beautiful color tone, light resistance, stability, and non-toxicity of Red Red Pigment as a red pigment, while maintaining low oil absorption and excellent dispersibility. An object of the present invention is to provide a red composite pigment and a method for producing the same. As a result of various studies, the present inventors have found that the above object can be achieved by forming a hematite particle layer by using silica-based particles as cores and depositing hematite particles on the surface of the particles, thereby completing the present invention. It came to this. Hematite as a composite pigment such as the one of the present invention and a method for producing the same have not yet been discovered. "Means for Solving the Problems" The present invention relates to a red composite pigment characterized by having silica-based particles as a core and a hematite particle layer formed on the surface thereof. Furthermore, the present invention provides a dry process for producing a red composite pigment, which is characterized in that a hematite particle layer is formed on the surface of the silica particles by pulverizing silica particles in the presence of hematite particles and depositing the hematite particles on the crushed surface. It concerns the manufacturing method. The present invention also provides a wet manufacturing method for a red composite pigment, which comprises forming a hematite particle layer on the surface of the silica particles by mixing, dispersing, and heating silica particles and hematite particles in an alkaline aqueous solution. It is related to. The present invention will be explained in detail below. The hematite particles used in the present invention are not particularly limited as long as they have a red pigment. The hematite used in the present invention can be produced by directly roasting iron compounds such as iron sulfate, or indirectly by dehydrating goethite (acicular, granular, rod-shaped, disc-shaped). Furthermore, hematite produced directly by a wet method may also be used. Generally, in order to adhere to silica-based particles, granular or disk-shaped particles are preferable. Hematite particles are orange-red at approximately 0.1 μm and 0.2 μm
The particle size is reddish-brown, and the particle diameter is purple-red at around 0.5 μm. Therefore, in order to exhibit a red color, a particle size of 0.1 μm to 0.6 μm is desirable. In the present invention, the silica particles act as a nucleus and contribute to the dispersibility of the pigment. It also acts as a bulking agent. From these points of view, it is desirable that the particle size of the silica-based particles as the core be in the range of 1 to 18 μm, preferably 3 to 15 μm. In the present invention, when used as a pigment, silica-based particles are preferably those that do not interfere with the red color of hematite, and generally transparent, white, or pale white particles are used. Silica-based particles used in the present invention, i.e. SiO ₂
Inorganic particles containing 15% by weight or more generally have a highly active particle surface, are light and inexpensive, or have a particle surface that exhibits activity through treatment and are easily adhered to. Examples include silica, soda lime glass, borosilicate glass, lead glass, and alkali-free glass. The hematite content in the red composite pigment according to the present invention is preferably from 5% by weight to 40% by weight, based on the specific surface area of silica particles and hematite particles. The particle size of the red composite pigment, which has the silica-based particles of the present invention as a core and has a hematite particle layer formed on its surface, can be changed depending on the size of the core used, the type of hematite, manufacturing conditions, etc. However, from the viewpoint of improving dispersibility, the thickness is 1 to 20 μm, preferably 2 to 17 μm. Red composite pigments can be produced by directly coating hematite particles on silica-based particles that serve as the core, or by heat-treating them at 250°C or higher after coating goethite particles in various particle forms on silica-based particles. You can even get it. The red composite pigment according to the present invention can be produced by either a dry method or a wet method, as detailed below. (1) Dry method: When silica particles or their agglomerates and hematite powder are mixed and crushed in a dry process, the hematite is so fine that it is not crushed any further, but the solid solution is crushed and a new surface is formed, and the hematite powder is formed on that surface. A red composite pigment with a hematite particle layer formed thereon is obtained. On a small scale, for example, when mixing and grinding are carried out using an automatic mortar, it is observed that silica-based particles easily become cores and hematite powder adheres to their surfaces. This phenomenon occurs because during dry mixing, contact and frictional electrification occur and work effectively for adhesion. Furthermore, since the surface of the silica-based particles immediately after grinding is extremely active and has strong adsorption properties, a mechanochemical reaction can be considered that allows fine hematite powder to be well adsorbed. These mechanisms are explained in Yamaguchi, Shikizai, ₅₈ , [8] 476 (1985). Industrially, for example, a centrifugal rotary ball mill is used. At this time, the adhesion effect is even better if it is carried out in dry air, an inert gas stream, or a vacuum. (2) Wet method: Put the core silica particles and hematite powder into an aqueous sodium hydroxide solution, mix well, and disperse. Next, heat while mixing and dispersing, usually at 50 to 90°C for 2 to 3 hours.
Then wash with water and dry. By this operation, it is possible to obtain a red composite pigment in which hematite powder is uniformly adhered to the surface of the silica-based particles to form a hematite particle layer. This adhesion phenomenon is thought to occur because the surface of the silica particles is slightly dissolved and eroded by the alkali, and a small amount of silicate such as sodium silicate acts as a glue, causing the hematite powder to adhere to the core surface. be done. As for the dispersion machine, an ultrasonic dispersion machine is good for small-scale use, but for more industrial use, for example, attritor (bead mill) is used.
etc. are suitable. (3) In the dry method or wet method of (1) and (2) above, goethite with a particle diameter (minor axis diameter in the case of needle-shaped particles) of 0.2 μm or less is coated on the silica particles, and this is heated at 250℃ or higher. The red composite pigment of the present invention can also be obtained by heat treatment at high temperature to convert it into hematite. The easily dispersible red composite pigment of the present invention obtained as described above is a novel pigment that improves the characteristics of conventional pigments and is a step forward. The red composite pigment of the present invention has a particle size of 1 to 20 μm, which is larger than conventional pigments, so it can be used as a non-toxic red pigment with particularly excellent dispersibility for paints, printing inks, synthetic resins, cosmetics, building materials, paints, etc. can be used. It is particularly applicable to make-up cosmetics, synthetic resins, cement, etc. that require easy dispersion. "Examples" The present invention will be explained in more detail below using Examples. Example 1 (Wet method) 3.0 g of granular hematite (average particle size 0.30 μm) was added to 50 ml of distilled water and dispersed using an ultrasonic disperser. 9 g of crushed silica (2-7 μm) was added to this dispersion, and after humidifying at 60°C, 2N was added to the dispersion while stirring.
150 ml of NaOH aqueous solution was added and stirred for 2 hours. The resulting red precipitate was washed with water, filtered, and dried to obtain a red composite pigment powder (hematite content: 25% by weight). When the coloring power of the obtained red composite pigment powder and hematite powder was examined based on the Japanese Industrial Standards Committee Pigment Test Method (JISK5101), the composite pigment was superior, and the oil absorption amount was also 10%.
% (22% hematite particles). Examples 2 to 4 The content of platy hematite (average particle size 0.25 μm) obtained from platy goethite in Example 1 was changed from 25% by weight to 15% by weight (Example 2) and 35% by weight (Example 3). It was prepared in the same manner as in Example 1, except that 50% by weight (Example 4) was changed. Examples 2 and 3 gave considerable tinting strength. The oil absorption amount was 9% in Example 2, 11% in Example 3, and 15% in Example 4. Example 5 (Dry method) Granular hematite similar to Example 1 (average particle size
0.30μm) 1.5g and crushed silica (2-7μm) 4.5g
was crushed for 30 minutes using a crusher to obtain a red composite pigment powder. Furthermore, when the coloring power and oil absorption of the obtained red composite pigment powder were examined based on the pigment test method, the coloring power was greater than that of the uncoated powder, and the oil absorption was also 13ml/1.
g and good results were given. [Comparative Example] A mixture of 3.0 g of granular hematite (average particle size 0.30 μm) and 9.0 g (2 to 7 μm) of crushed silica was examined for coloring power, oil absorption, and hiding power based on the pigment test method. Table 1 shows a comparison between Example 5 (dry method) and Example 5 (dry method).

[Table] "Effects of the Invention" As is clear from the above, according to the present invention, the color tone, weather resistance,
It is possible to produce an excellent new red composite pigment that maintains stability and non-toxicity, is easily dispersed even in a powder state, and is hydrating. The red pigment according to the present invention is more suitable for coloring various materials including basic cosmetics used in powder form.

Claims (1)

[Scope of Claims] 1. A red composite pigment characterized in that the core is an inorganic particle containing 15% by weight or more of _SiO2 , and a hematite particle layer is formed on the surface of the core. 2. The red composite pigment according to claim 1, wherein the inorganic particles have a particle diameter (average) of 1 to 18 μm. 3. The red composite pigment according to claim 1, wherein the hematite particles are granular, spherical, plate-shaped, needle-shaped, or disc-shaped, and have a particle diameter of 0.5 μm or less. 4 Hematite content in the red composite pigment is 5~
40% by weight of the red composite pigment according to claim 1. 5. The red composite pigment according to claim 1, wherein the red composite pigment has an average particle diameter of 1 to 20 μm. 6. The red composite pigment according to claim 1, wherein the inorganic particles are one or more selected from the group consisting of silica, soda lime glass, borosilicate glass, lead glass, and alkali-free glass. . 7. In the presence of hematite particles, inorganic particles containing 15% by weight or more of SiO ₂ or agglomerates thereof are crushed, and the hematite particles are adhered to the crushed surface to form a hematite particle layer on the surface of the inorganic particles. A dry manufacturing method for a red composite pigment, characterized by forming a red composite pigment. 8 A red color characterized by forming a hematite particle layer on the surface of the inorganic particles by mixing, dispersing, and heating inorganic particles containing 15% by weight or more of SiO ₂ and hematite particles in an alkaline aqueous solution. Wet manufacturing method for composite pigments.