JPH01271477A - Abrasive grain and its production - Google Patents

Abstract

PURPOSE:To obtain abrasive grains having a high affinity for a binder and excellent electrical insulation property by disintegrating abrasive grains immersed in silica sol to the size of the initial abrasive grains, removing silica particles from the particles, heat-treating the remaining particles and quenching them. CONSTITUTION:Abrasive grains are immersed in silica sol and excess silica sol is separated from the particles. The resulting particles are dried and disintegrated to the size of the initial grain size, and silica particles are removed therefrom by heavy liquid separation. The remaining particles are heat-treated at 700-1100 deg.C in air and quenched to obtain the purpose abrasive grains. Although a relatively low temperature such as 300 deg.C is effective for the heat treatment, a temperature >=700 deg.C is necessary to impart sufficient electrical insulation property to the grains. However, heat treatment at a high temperature above 1100 deg.C should be avoided except the case where no sufficient strength is necessary, because the strength of the SiO2 film is lowered. When the quenching is performed in air immediately after the heat treatment, the SiO2 can be prevented from crystallizing, and abrasive grains coated with glassy SiO2 can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application J] The present invention relates to novel abrasive particles with improved surface properties. More specifically, it relates to abrasive particles whose surfaces are coated with a thin film of tortoiseshell silica, which has a high affinity with various binders and excellent electrical insulation properties, making them particularly suitable for use in electroplated grindstones. relating to abrasive particles.

[Prior art] Abrasive materials are used as materials for scraping or abrading objects by using minerals with large lumps, and at first natural products were used, but in N. In search of this katata, most of the materials have come to be made of man-made materials. (In this application, both grinding and polishing are referred to as polishing.) The developed materials include highly purified natural products and non-natural cubic boron nitride (hereinafter referred to as CBN). Abrasives with excellent flatness and toughness are now available.

However, no matter how good the particles are, the quality of the abrasive tool produced by bonding the particles depends in large part on the bond strength achieved. In other words, for the quality of the abrasive particles to be expressed in the abrasive tool, it is extremely important that the particles are firmly held in place, which naturally requires high bond strength. In fact, the harder and therefore more durable the abrasive particles, the greater the demands on bond strength. That is, when extreme hardness is present, the particles have less tendency to fracture or abrade and therefore have a greater tendency to pull away from their bonds under the severe forces during grinding. Abrasive particles therefore require a high degree of bond strength between the particles and the binder in order to achieve maximum benefits in hardness.

For this reason, for example, in the case of CBN, in order to improve its affinity with the binder, the abrasive grains are first heated at 775°C in the air.
B on the surface by heat treatment at ℃ conditions.

There is a method (Japanese Patent Publication No. 48-23589) in which 03III is prepared, further immersed in an organosilicon compound solution, and then heated at about 500°C to form a borosilicate liquid film on the surface.

Additionally, there is a known method (Japanese Patent Application Laid-Open No. 149811/1983) in which cubic boron nitride abrasive grains, which contain metallic boron and have reduced electrical insulation properties, are treated with acid to remove the boron on the surface and impart insulation properties. There is.

On the other hand, a proposal for metal-coated abrasive particles with a large number of concave holes (
JP-A-59-30671).

Separately, the present inventors vacuum-heated an Si-5iO□-based green compact to form SiOx (2≧
Proposed abrasive grains coated with a thin film of χ≧0 (Patent application 1986-
(hereinafter referred to as the "first application").

However, the invention of the aforementioned Japanese Patent Publication No. 48-23589, CB
JP-A-57-149811 cannot be applied to abrasive grains other than N, and heat-treating the abrasive grains twice reduces the strength of the abrasive grains, which is undesirable from an economic point of view. It is limited to abrasive grains that contain soluble acid content. The invention of JP-A-59-30671 is limited to metal-coated abrasive grains, and these abrasive grains cannot be used in electrodeposited grindstones. Therefore, the invention in the earlier application does not have these problems.
We have proposed an abrasive particle that can be applied to all types of binders and a method for producing abrasive particles that is not limited by the type of abrasive particle or binder.

ff1ll that the L invention seeks to solve SiOx (2≧χ≧0) II obtained in the previous application
The thickness of I is approximately 0.1 μm. This is sufficient if the only issue is affinity with the binder, but in order to further improve the strength of the binder, the surface!
It is preferable to have a rough shape.

On the other hand, when making an electrodeposited grindstone by the electrolytic method, the thickness of the SiOx (2≧χ≧0) film is approximately the same, and the withstand voltage of the film is about io'V/c, so the vapor deposition method alone is sufficient. However, in the case of a vapor-deposited film, the thickness may locally become <0.1 μm, so it is preferable to further coat another insulating film on top of this.

Moreover, if it is a single layer, it is preferable that the film thickness is 0.1 micrometer or more at the lowest part.

[Means for Solving the Problems] As stated in the previous application, SiO2 has good affinity with the binder of the abrasive particles and has high electrical insulation properties.

Colloidal silica (Ceramic 赳[4], 28G+'851) is commercially available as a suitable material for forming a SiO film on the surface of an article by coating it, and when this is used as a coating agent, It has excellent characteristics such as good adhesion of the coating film to the base material, strong and transparent properties, and the inherent color and transparency of the base material are not impaired.

However, it is generally difficult to apply this to coating abrasive grains, which are aggregates of fine grains.
A very important issue is how to obtain abrasive grains made only of ns and not mixed with fine grains.

The present invention solves this problem as follows.

That is, grinding abrasive grains are dispersed in colloidal silica (21 degrees Celsius is not particularly limited; use a commercially available approximately 20% solution or appropriate dilution thereof), and then this dispersion is evaporated to dryness. After completely removing moisture, the abrasive is crushed to approximately the original particle size, and single particles of silica are removed by a heavy liquid separation method.

Through the above steps, abrasive grains with silica attached having a complicated shape can be obtained, but if electrical insulation is an issue, it is preferable to further heat treat the abrasive grains.The heat treatment temperature is 30°C.
Although it is effective at a relatively low temperature such as 0°C, a temperature of 700°C or higher is required to obtain sufficient electrical insulation. However, high-temperature heat treatment exceeding 1100° C. deteriorates the strength of the SiO□ coating, so it should be avoided except for sharpening that does not require strength.

It should be noted that dry abrasive grains that have been treated with silica sol can be crushed and separated from a heavy liquid after heat treatment to obtain abrasive grains of almost the same quality.

Immediately after this, quenching in the atmosphere can prevent the crystallization of SiOw, resulting in a glassy SiOv-coated abrasive.
grains (can be)

If the abrasive grains are hydrophobic in nature, this can be overcome by the addition of surfactants, but S
SiOx (
2≧χ≧0) If the method of the present invention is applied after applying a film (including post-oxidized films), strongly bonded S i O
W-coated abrasive grains are obtained. In particular, unlike the vacuum deposition method, the abrasive grain coating obtained by the method of the present invention is
The abrasive grains have many cracks or wrinkles on the surface, and the shape of the abrasive grains has a fractured surface with many irregularities due to crushing, and the abrasive grains have even higher bondability with the bond from a mechanical point of view.

Furthermore, when using the method of the present invention, compared to the vapor deposition method.

It is possible to obtain abrasive grains with a SiOz coating several times to several tens of times thicker.

[Function] Silica sol is made up of fine particles of silica on the order of 10 mμ dispersed in water.Since the silica contained is fine particles, its specific surface area is extremely large, 30 to 500 m''/g, and the surface of other substances is very large. It is estimated that silica is easily adsorbed to SiOx (2≧χ≧0
), SiOx (2≧χ≧0) becomes neutral [bonding coat] and adsorption is promoted.

Next, it is thought that the coated silica loses the water molecules interposed between the fine particles as it dries, resulting in a surface with a complex shape.

The reason why the electrical insulation properties are improved by heat treatment is that there are silanol groups (〉si-OH) on the coating surface that cannot be removed by drying at about 100℃, and these are involved in electrical conduction, but heat treatment at 700℃ or higher It is estimated that most of it will be lost.

[Example] The present invention will be specifically explained below using Examples.

(Reference example) In order to measure the electrical resistivity of colloidal silica, only the colloidal silica was evaporated to dryness without adding any abrasive grains, crushed, and then a portion of 302 μ to 127 μ was taken out, and a predetermined amount was placed in the atmosphere. After being heated to a certain temperature, it was immediately taken out of the furnace and its electrical resistivity was measured. The measurement method is lO
300DX10IDX with φ×IO plug
Table 1 shows the results of measurements by inserting 0.2 g of a sample into 8 volumes of No. 20 hard rubber, inserting a plunger of the same material and size as the stopper, and applying a light pressure of 50 V to whitening.

From Table 1, it can be seen that heat treatment at 700° C. or higher is necessary to obtain sufficient electrical insulation. Further, the upper limit of the heat treatment temperature is approximately 1100° C. since the strength of the coating deteriorates.

Table 1 Electrical specific resistance of heat-treated colloidal silica products (Example 1) ]00+nJ2 beaker with black silicon carbide abrasive material Cm
0.5 g of 80 was taken and about 2 me of colloidal silica with a solid content of 20% was added. After stirring thoroughly, the mixture was transferred to a filter paper under suction on a futschier, spread thinly, excess silica gel was removed, and the mixture was transferred to a dryer together with the filter paper, and dried at 100° C. for 60 minutes.

After cooling, Cm80 with silica sol attached was peeled off from the filter paper, crushed in an alumina mortar, and sieved to obtain 302
A ~151μ section was taken. This particle size portion was then mixed with ethylene bromide (specific gravity 2.18) about 50rrF2 to 1 OO,m 1. The mixture was placed in a beaker and stirred to remove individual silica gel particles as a suspension.

The portion settled at the bottom of the beaker was washed with ethanol, dried, transferred to an alumina boat, heated to 700° C. in a Matsufuru furnace, and then rapidly cooled.

When the electrical resistivity of 0.2 g of the sample thus obtained was measured using the method described above, it was found to be 50Vt'5.0XI.
O"Ω-cw (original sample C#80 is 7.4X10"Ω・
Cm) and the coating effect were clarified.

(Example 2) Cubic boron nitride abrasive grains containing excessive boron (particle size #80) 0
．． Spread 5g on a Mo board, set a tungsten basket about 50mm above this MoJN, and place SiOz
Approximately 100 mg of the evaporation source of the equimolar mixture green compact of
The mixture was filled into a basket and subjected to vacuum operation at about 1750°C under a vacuum of 10-' to IQ-' Torr in a conventional manner.

One operation took about 1 minute, and this operation was repeated 8 times. In addition, each time the operation was completed, the cubic boron nitride on the Mo plate was collected on the medicine wrapper paper and spread again.

After coating with a SiO film by vapor deposition in this way, it was coated with SiO It can be seen that the withstand voltage characteristics of the invented product are improved.

(Left below) (Example 3) Using the coated droplets obtained in Example 2, approximately lOφ
A test was conducted by electrodepositing nickel on the base metal (545G). The electrolyte is a sulfamate nickel solution, liquid temperature is 60℃,
Although the test was carried out at a voltage of 1 V for 60 minutes, no nickel balls were deposited on the Ni plating on the grain surface. On the other hand, numerous nickel balls were observed in the cubic boron nitride abrasive grains containing an excessive amount of boron and which were not coated at all.

[Effect] When abrasive grains are used as a tool such as a whetstone, it is common practice to make the surface of the abrasive grains into a complex shape to improve the bondability with the binder (for example, as described in JP-A-59-30671 mentioned above).
), although no particular explanation is required here, in the present invention such surface properties are achieved by coating with silica.

The surface properties when coated with silica are as shown in the enlarged photograph.

Furthermore, a feature of the silica coating method according to the present invention is that a thick film of several microns to several tens of microns can be obtained relatively easily. Therefore, such coated particles can generally be used in applications requiring high electrical insulation.

[Brief explanation of the drawing]

Claims (4)

[Claims] (1) Abrasive particles having a thin film of silica with tortoise-shell-like wrinkles on the surface. (2) Abrasive grains are soaked in silica sol, excess silica sol is separated, dried, crushed to almost the original grain size, silica single particles are removed by heavy liquid separation method, and then heated to 700°C in the atmosphere. A method for producing abrasive particles, characterized by heat treatment at ~1100°C and rapid cooling. (3) Soaking the abrasive grains in silica sol, separating excess silica sol, drying, heat treatment at 700°C to 1100°C, rapid cooling, crushing, and then removing single silica particles by heavy liquid separation method. Characteristic method for producing abrasive particles. (4) A method for producing abrasive particles, characterized in that abrasive grains coated with SiO_χ (2≧χ≧0) by a vapor deposition method are subjected to the treatments described in items 2 and 3 above.