JPS6016400B2 - Manufacturing method of corundum grains - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to the production of spherical polyhedral corundum grains with extremely uniform particle diameters for use as smoothers for liquid crystal display elements, fillers for magnetic coatings, abrasive grains for polishing films, abrasive grains for precision lapping, etc. It concerns the manufacturing method.

As is well known, the gap between the electrode glass plates of a liquid crystal display element is
Suitable for fixing to a constant value between 15 degrees, filler for adding wear resistance to the magnetic coating of magnetic tapes and magnetic disks, and abrasive film and tape for wrapping, or precision free wrapping. The abrasive used requires ceramic powder with a much more uniform particle size than normal abrasives.

Conventionally, ceramic powders used in such fields are produced by finely pulverizing and classifying hard and chemically stable substances such as corundum, garnet, chromium oxide, and silicon carbide, or by classifying the powder from Bayer alumina. Powders of these substances obtained by high-temperature firing are either used as they are or are further pulverized and then classified.

However, since the powders obtained by these methods all have random shapes that are far from spherical, there is an inherent limit to uniformizing the particle size through classification.
In addition, a method of obtaining a uniformly shaped abrasive using single crystal grains of corundum using a hydrothermal method, as seen in Jiko Sho 37-7750, has also been attempted; However, it is difficult to control the direction of the arrangement, which makes it undesirable for the above-mentioned applications.

Tokuseki 1973 Kawa 1 School Specification 9 describes the application of single-crystal corundum grains produced by hydrothermal method to an abrasive film;
Similar to 7-7750, corundum seed crystals are not used in the hydrothermal treatment, so the corundum grains obtained are generally a mixture of plate-like or columnar grains and particles in which single crystals thereof aggregate. A problem arises. The present applicant previously proposed Tokkeki Sho 52-1 Sekisho as a method for improving the grain shape, etc. of corundum grains produced by a hydrothermal method.

This method involves uniformly mixing a predetermined amount of corundum fine particles into the raw material alumina hydrate in advance and subjecting the mixture to hydrothermal treatment. According to this method, a spherical polyhedral corundum single crystal is obtained, and its particle size can be freely controlled, and the particle size distribution is very narrow compared to a method that does not use corundum fine particles. It was found that the spherical polyhedral grains contained a considerable amount of agglomerated particles, and that further post-treatment was required for the above-mentioned special uses. According to our research, it is desirable that the particle shape factor be 1.3 or less for smoothers for liquid crystal display elements, fillers for magnetic coatings, precision lapping materials, and the like. Here, the shape factor is determined by calculating the average value of the ratio of the major axis of each grain to the minor axis orthogonal to the major axis (major axis/minor axis) determined by the microscope magnification method of JISR6002. Therefore, if there are only perfectly spherical particles, the shape factor is 1, and it can be said that the closer the shape factor is to 1, the more spherical the particle is. Suitable for materials, etc., with uniform particle size and shape factor of 1
．． The purpose of this method is to add corundum particles to an alumina hydrate and perform hydrothermal treatment to prevent the formation of new corundum crystal nuclei while creating a surface of the added corundum particles. The process consists of precipitating alumina in alumina hydrate as corundum, crushing the resulting corundum particles, and then classifying them into dispersed particles with a shape factor of 1.3 or less. The method of this invention will be explained in detail below. The method and essence of our earlier application, JP-A-52-15498, regarding the hydrothermal treatment of adding corundum particles as seed crystals to raw material alumina hydrate to prevent the generation of new corundum crystal nuclei. There is nothing that has really changed. That is, the alumina hydrate may be either aluminum hydroxide (trihydrate) or boehmite (monohydrate), and the amount of corundum added to the alumina hydrate is determined in terms of trihydrate. The total weight of alumina hydrate is W
R (Yu) and the total area of the seed crystal corundum to be added is A
Assuming s (earth), the WR/As value is preferably 0.05 m/m or less, particularly preferably 0.02 m/m or less. Here, As (base) can be determined by magnification microscopy according to JISR6002. In addition, mixing alumina hydrate and corundum fine particles sufficiently;
Further, in the hydrothermal treatment, it is desirable to reduce the temperature difference in the raw materials as much as possible, as described above. The temperature and pressure of water treatment are 370-500 and 0,150-5
A range of 00k9/earth is appropriate. Hakama Kaisho 52-1549 states that if hydrothermal treatment is carried out under these conditions, corundum crystal grains with at least a single particle having a spherical polyhedral shape can be obtained, and that the single particle diameter can be controlled relatively easily.
As stated in 8.

Subsequently, the present inventor conducted further research and investigated the morphology of corundum grains obtained by this method. As a result, a portion of the corundum grains existed as agglomerated grains, which were caused by the growth of nearby seed crystals. They come into contact during the process and adhere to each other through grain boundaries, and their adhesion is not as strong as that of fired grains, and the diameter of the adhering surface is about 2 times that of a single particle flea.
/3 to 1/3, and it was found that it is possible to disintegrate into single particles of spherical polyhedron with relatively weak force.
Therefore, various studies were conducted on methods of destroying only the attached parts of the spherical polyhedron without destroying the single particles. As a result, mills that have a grinding action between particles without impact, such as rod mills that increase the filling rate of rods and treated granules in the pot and reduce the rotation speed, or It has been found that scales can be effectively used to disintegrate agglomerated particles in the present invention by using a container-type powder processing apparatus. The crushing time varies depending on the processing equipment used, but generally 20 to 200 minutes is sufficient. Although there is no particular restriction as to whether to select dry or wet crushing conditions, dry crushing is generally preferred in terms of preventing contamination of the corundum grains. The corundum particles obtained in this way are spherical polyhedral particles containing almost no agglomerated particles, and at this stage the particle distribution is quite narrow. By applying this, it is possible to obtain dispersed particles of a predetermined particle size with a precision not found in conventional corundum particles.

The corundum particles obtained by the above method have a shape factor of 1.3 or less, are mostly composed of spherical polyhedrons, and have extremely uniform particle sizes, so they have characteristics not found in conventional ceramic powders. .

Since the surface layer of the seed crystal of this corundum grain is a single crystal, if single crystal corundum is used as the seed crystal, the entire grain becomes a single crystal. Corundum, which is not a single crystal, can also be used as a seed crystal.
In this case, the seed crystal, which is not a single crystal, is wrapped in a single crystal growth layer, so even if the seed crystal is distorted, the grain as a whole behaves in the same way as a single crystal, which is advantageous.
It is preferable that particles for substrates for liquid crystal display elements, fillers for magnetic coatings, and particles for precision wrapping have a small difference in height (or thickness) between particles when they are placed randomly on a flat surface, but the present invention Corundum particles can be said to best satisfy this condition. Furthermore, since it does not contain aggregated particles, the particles do not decompose during use and can maintain a stable state. Example 1 2.4% by weight of Bayer alumina (corundum) fine particles with a particle size of 1 to 4r were added to aluminum hydroxide powder 50k9 obtained from the Bayer process (WR/As: 0.00
After 56 days/day), the mixed raw materials were mixed uniformly, and the mixed raw materials were
Filled in a stainless steel container with 8 yards and 1.4 meters depth, and used an autoclave with an internal volume of 50, 45,000,4
Hydrothermal treatment was carried out at 50k9/m for 6 hours to obtain corundum grains A with mottling K9.

Next, put A's 3K9 into a rod mill filled with European steel rods with an outer diameter of 2 mm and a length of 245 mm to a porosity of 42% in a mild steel pot with an inner diameter of 25 mm and a depth of 25 mm. After carrying out a dry treatment for 130 minutes at a rotation speed of the pot at a rotation speed of 4/min, pickling and water washing were performed to obtain corundum grains B of 2.9k9. On the other hand, J made of pulverized particles of fused alumina
ISW^#250 ratio was prepared, and the classification points for each of the three types of corundum grains, together with A and B, were set at 6 and 81' in terms of Stokes diameter, and sedimentation separation treatment by Suikan was performed. , A', B', and 〇, respectively, were obtained. Next, for each of A', B', and C', the particle shape was observed, and by microscopy according to JISR6002, the particle size distribution, average flea, and ratio of the major axis of each grain to the minor axis perpendicular to this were determined. The average value was calculated, and the shape factors for A', B', and 〇 were determined.

The above measurement results are shown in Table 1. Table 1 Example 2 Aluminum hydroxide obtained from the Bayer process was
2. Add JISW^#4000 corundum fine grains to powder 45k9 which has been treated with 80qo, 10.2k9/me for 2 hours to form boehmite. Base weight% added (WR/As: 0.0
099/K) The homogeneously mixed raw materials were hydrothermally treated in exactly the same manner as in Example 1 to obtain 37k9 corundum grains D.

Next, 3k9 of D was put into a rod mill in the same manner as in Example 1, and after dry treatment for 4 minutes at a rotational speed of 4 m/min, the corundum grains E of 2.9k9 were obtained. . On the other hand, JISW^150 is made of pulverized fused alumina.
0F was prepared, classification points of 9 and 11 were set for each of these three types of corundum grains, D, E, and F, and Shiotsubobee separation processing was performed using a water mirror, resulting in 〇, E', and F', respectively.
Three types of classified products were obtained. Next, each of 0, 8, and F' was observed and measured in the same manner as in Example 1, and the results shown in Table 2 were obtained.

Table 2 As is clear from Tables 1 and 2, the corundum grains produced by the method of the present invention have a higher degree of uniformity in particle size than conventional corundum grains made of crushed grains or agglomerated grains, and have a shape factor of 1.3. The corundum grains are nearly spherical as shown below.

Claims (1)

[Claims] 1 Corundum fine particles are added to alumina hydrate and subjected to hydrothermal treatment, and the alumina in the alumina hydrate is precipitated as corundum on the surface of the added corundum fine particles while preventing the generation of new corundum crystal nuclei. A method for producing corundum grains, which comprises crushing corundum grains and then classifying them to obtain dispersed particles having a shape factor of 1.3 or less.