JP2003064350A - Method for producing cubic boron nitride abrasive grain - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide cubic boron nitride abrasive grain capable of forming a whetstone having excellent cutting quality, and to provide a method for producing the abrasive grain. SOLUTION: This cubic boron nitride abrasive grain is obtained by maintaining a mixture comprising hexagonal boron nitride and seed crystal of cubic boron nitride under a pressure and temperature condition where the cubic boron nitride is thermodynamically stable, wherein twin crystal of the cubic boron nitride is included in the seed crystal of the cubic boron nitride. The obtained cubic boron nitride abrasive grain is crushed with a roller crusher.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cubic boron nitride abrasive grain manufacturing method and cubic boron nitride abrasive grain used for a grindstone or the like.

[0002]

2. Description of the Related Art Cubic boron nitride has hardness second only to diamond and chemical stability surpassing that of diamond, and the demand for abrasive grains for grinding, polishing and cutting materials is increasing.

Various methods for producing cubic boron nitride have been devised. Among them, the best known method and widely used industrially are hexagonal boron nitride in the presence of a catalyst substance and the like. At about 4-6 GPa, about 1400-1600 ° C
It is a method of maintaining hexagonal boron nitride in the thermodynamically stable region of cubic boron nitride to some extent and directly converting hexagonal boron nitride into cubic boron nitride (for example, Japanese Patent Publication No. 59-39362).
For example, Japanese Patent Publication No. 3-14495, Japanese Patent Publication No. 3-47132, and Japanese Patent Publication No. 3-15488 can be exemplified. ).

The cubic boron nitride abrasive grains obtained by these methods have excellent hardness and chemical stability as described above, and are also used in electrodeposition grindstones, metal bond grindstones and the like.

[0005]

The cubic boron nitride abrasive grain obtained by the above-mentioned method is a blocky abrasive grain having a shape relatively close to a sphere, and a vitrified bond grindstone requiring sharpness is used. It was not suitable for grinding applications.

For this reason, Japanese Patent Application Laid-Open No. 9-169971 discloses, in order to improve the sharpness of a grindstone using cubic boron nitride abrasive grains, "cubic boron nitride particles having a sharp shape and a relatively dense meat quality". It is disclosed that "good sharpness is maintained" by using "." However, the grindstone using cubic boron nitride abrasive grains obtained by this method has improved sharpness of the grindstone compared to the case of using the conventional blocky-shaped abrasive grains, but from the industrial world a sharper grindstone Was required.

In terms of the grindstone, the binder in the vitrified bond grindstone is melted during firing to fuse the gaps between the abrasive grains, and exhibits a strong bonding force after cooling. In order to obtain a good sharpness in a porous grindstone such as a vitrified bond grindstone, it is necessary to increase the number of pores.

However, when the amount of the bonding material is decreased to increase the pores, the force for holding the abrasive grains is weakened, and the abrasive grains are more likely to come off due to the load during grinding. As a result, the surface roughness of the work material is reduced and the dressing interval is shortened, so that a sufficient grinding ratio cannot be obtained. Also,
When the abrasive grain ratio is reduced, the holding power of the abrasive grains by the binder is sufficient, but the hardness of the grindstone decreases due to the decrease in the bridges between the abrasive grains, and the load at the time of grinding cannot be withstood. Since the amount of falling off increases, a sufficient grinding ratio cannot be obtained.

As a method for solving these problems, a method of compensating for the reduced amount of abrasive grains and bonds by adding an aggregate has been proposed, but when the aggregate is added, the pores in the grindstone are reduced and the sharpness is improved. Was hindering the improvement of

[0010]

Means for Solving the Problems As a result of diligent efforts and studies to solve the above problems, the present inventor has found that in a method for producing cubic boron nitride abrasive grains using an ultrahigh pressure method, cubic boron nitride It has been found that by using a multiple twin crystal as a seed crystal, cubic boron nitride abrasive grains (“abrasive grains” may be simply referred to as “grains”) having a shape suitable for a vitrified bond grindstone can be obtained. Completed the invention.

That is, the present invention relates to the following: (1) A cubic boron nitride abrasive grain is obtained by maintaining a mixture containing hexagonal boron nitride and a seed crystal of cubic boron nitride under a pressure-temperature condition that is thermodynamically stable for cubic boron nitride. A method for producing cubic boron nitride abrasive grains, wherein the seed crystal of cubic boron nitride includes twin crystals of cubic boron nitride. (2) A method for producing a cubic boron nitride abrasive grain, which comprises pulverizing the cubic boron nitride abrasive grain produced by the method for producing a cubic boron nitride abrasive grain as described in 1 above. (3) The method for producing cubic boron nitride abrasive grains according to item 2, wherein a roll pulverizer is used for pulverizing the cubic boron nitride abrasive grains. (4) From the cubic boron nitride abrasive grains manufactured by the method according to any one of the preceding items 1 to 3, the triaxial major axis of the cubic boron nitride abrasive grains is L (μm), and the thickness is T (μm). The method for producing cubic boron nitride abrasive grains is characterized in that the abrasive grains having L / T of 1.5 or less are removed. (5) A cubic boron nitride abrasive grain produced by the method for producing a cubic boron nitride abrasive grain according to any one of items 1 to 4 above.

[0012] (6) In the cubic boron nitride abrasive grains, the bulk specific gravity (unit: g / cm ³⁾ cubic a, is calculated by dividing the true density of cubic boron nitride (3.48 g / cm ³⁾ The filling rate of the crystalline boron nitride abrasive grains is the particle size classification defined in JIS-B4130,

With a 40/50 abrasive grain, 0.482-
Within the range of 0.282, with 50/60 abrasive grains, 0.4
In the range of 80 to 0.280, 60/80 abrasive grains,
In the range of 0.478 to 0.278, in the case of 80/100 abrasive grains, in the range of 0.474 to 0.274, 100/12
In the case of 0 grain, within the range of 0.469 to 0.269, 12
0/140 abrasive grains are in the range of 0.464 to 0.264, and 140/170 abrasive grains are in the range of 0.459 to 0.25.
In the range of 9 and 170/200 abrasive grains, 0.453-
In the range of 0.253, 200/230 abrasive grains, 0.
In the range of 446 to 0.246, in the case of 230/270 abrasive grains, in the range of 0.440 to 0.240, 270/325
For the abrasive grains of No. 3, within the range of 0.433 to 0.233, 325
/ 400 abrasive grains are in the range of 0.426 to 0.226, and are cubic boron nitride abrasive grains.

(7) The cubic boron nitride abrasive grains as described in 6 above, wherein the cubic boron nitride abrasive grains are substantially monocrystalline.

(8) A grindstone produced by using the cubic boron nitride abrasive grains according to any one of the above 5 to 7 and a binder. (9) The grindstone according to the above item 8, wherein a vitrified bond is used as the binder. (10) The compounding amount of vitrified bond in the grindstone is 1
The above item 9 characterized in that it is in the range of 0 to 30% by volume.
The whetstone described in. (11) The abrasive grain ratio in the grindstone is ((cubic boron nitride abrasive grain filling rate−0.1) × 100) volume% to ((cubic boron nitride abrasive grain filling rate + 0.05) × 100. ) Any one of the above items 8 to 10, characterized in that it is within a volume% range.
The whetstone according to item. (12) Abrasive grain ratio in the grindstone is ((cubic boron nitride abrasive grain filling factor−0.05) × 100) volume% to ((cubic boron nitride abrasive grain filling factor + 0.05) × 100. ) The grindstone according to any one of items 8 to 10 above, which is in a volume% range.

(13) A polishing cloth paper produced by fixing the cubic boron nitride abrasive grains according to any one of items 5 to 7 above to a cotton cloth or a cloth equivalent thereto with an adhesive.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The cubic boron nitride abrasive grain of the present invention has a bulk specific gravity (unit: g / cm) of the cubic boron nitride abrasive grain.
³ ) is the true density of cubic boron nitride (3.48 g / c
m ³ ), the packing ratio of cubic boron nitride abrasives obtained by dividing by m ³ ) is a particle size classification defined in JIS-B4130,

With a 40/50 abrasive grain, 0.482-
Within the range of 0.282, with 50/60 abrasive grains, 0.4
In the range of 80 to 0.280, 60/80 abrasive grains,
In the range of 0.478 to 0.278, in the case of 80/100 abrasive grains, in the range of 0.474 to 0.274, 100/12
In the case of 0 grain, within the range of 0.469 to 0.269, 12
0/140 abrasive grains are in the range of 0.464 to 0.264, and 140/170 abrasive grains are in the range of 0.459 to 0.25.
In the range of 9 and 170/200 abrasive grains, 0.453-
In the range of 0.253, 200/230 abrasive grains, 0.
In the range of 446 to 0.246, in the case of 230/270 abrasive grains, in the range of 0.440 to 0.240, 270/325
For the abrasive grains of No. 3, within the range of 0.433 to 0.233, 325
With an abrasive grain of / 400, it is within the range of 0.426 to 0.226.

The filling rate of the cubic boron nitride abrasive grains conventionally used is higher than the filling rate of the abrasive grains of the present invention, and in order to obtain the abrasive grain holding force of the grindstone using the cubic boron nitride abrasive grains. In this case, it was necessary to obtain a sufficient bridge between the abrasive grains, and as a result, the abrasive grain ratio could not be lowered while maintaining the grinding ratio.

It has been clarified that by using the cubic boron nitride abrasive grains having the filling rate of the present invention, a sufficient bridge can be obtained between the abrasive grains even if the abrasive grain rate of the grindstone is reduced.
As a result, even if the abrasive grain ratio was reduced, the retaining force of the abrasive grains in the grindstone did not decrease, the abrasive grains were prevented from falling off, and the grinding ratio was significantly improved. In addition, the porosity of the grindstone was increased, and the sharpness was greatly improved. The filling rate of the cubic boron nitride abrasive grains in the present invention is obtained by dividing the bulk specific gravity of the cubic boron nitride abrasive grains by the true density of the cubic boron nitride grains. The bulk specific gravity is measured according to JIS-R6126 "Test method for bulk specific gravity of artificial abrasives".

The measuring method will be described below. The outlet of the funnel was closed with a stopper, and the measurement sample was 20.0 ± 0.1.
Place g in the funnel. A cylinder with a volume of 8.0 ± 0.1 ml is placed just below the funnel outlet (falling distance from the funnel outlet to the top of the cylinder is 95.0 ± 1.0 mm). After pulling out the stopper and dropping the whole amount of the sample into the cylinder, the sample rising from the upper surface of the cylinder is removed by scooping using a metal plate. Next, the mass of the sample remaining in the cylinder is measured and divided by the cylinder volume to obtain the bulk specific gravity.

The bulk specific gravity is measured by the above method,
In order to accurately measure the bulk specific gravity, it is necessary to wash the abrasive grains with dilute hydrochloric acid or aqua regia before measurement, deoxidize and dry them in order to remove the effects of deposits and dirt on the surface of the abrasive grains. is there. The cubic boron nitride abrasive grain of the present invention is J
The cubic boron nitride abrasive grains have a filling rate within the above-mentioned range in the particle size classification defined by IS-B4130, but may be used by blending in a plurality of particle size classifications. Further, the cubic boron nitride abrasive grains having the filling rate of the present invention may be re-classified and used according to another grain size classification, and JIS-B4130.
The particle size may be reclassified by a method different from.

The method of synthesizing the cubic boron nitride abrasive grains used in the present invention is not particularly limited, but considering productivity, hexagonal boron nitride is used in the presence of a catalytic substance to stabilize the cubic boron nitride thermodynamically. A method of holding in the region to convert hexagonal boron nitride to cubic boron nitride is desirable.

As the starting material, hexagonal boron nitride, a commercially available hexagonal boron nitride powder can be used. Oxygen impurities mixed in the form of boron oxide or the like may delay the conversion of hexagonal boron nitride to cubic boron nitride, and therefore, those having a small amount of oxygen are preferable. The particle size is not particularly limited, but in general, the particle size defined in JIS-R6001 is preferably 150 mesh or less. This is because if the particle size is too large, the reactivity with the catalyst substance may decrease.

The catalyst used in the method of converting hexagonal boron nitride into cubic boron nitride is not particularly limited, and all known catalysts can be used. For example, alkali metal (Li
Etc.) and their nitrides (Li ₃ N, etc.) and boronitrides (Li ₃ BN _2, etc.), alkaline earth metals (Ca, Mg, S)
r, Ba, etc.) and their nitrides (Ca ₃ N ₂ , Mg
₃ N ₂ , Sr ₃ N ₂ , Ba ₃ N _2, etc.) and boronitride (Ca ₃
B ₂ N ₄ , Mg ₃ B ₂ N ₄ , Sr ₃ B ₂ N ₄ , Ba ₃ B ₂ N
₄ etc.), and a composite boronitride of alkali metal and alkaline earth metal (LiCaBN ₂ , LiBaBN _2, etc.) can be used. The particle size of the catalyst is not particularly limited, but 150 mesh or less is preferable. This is because if the particle size of the catalyst is too large, the reactivity with hexagonal boron nitride may decrease. The mixing ratio of the catalytic substance to hexagonal boron nitride is
It is preferable to mix the hexagonal boron nitride in an amount of 5 to 50 parts by mass as a catalyst substance with respect to 100 parts by mass. As a method of coexisting the catalyst substance and hexagonal boron nitride, there is a method of mixing these powders, but the hexagonal boron nitride layers and the catalyst substance layers may be arranged to be alternately laminated in the reaction vessel. .

In practice, after mixing the hexagonal boron nitride and the catalyst substance, or separately, 1 to 2 ton /
It is preferable to fill the reaction vessel after molding at a pressure of about cm ² . By doing so, the handling property of the raw material powder is improved, the shrinkage amount in the reaction vessel is reduced, and the productivity of the cubic boron nitride abrasive grains is improved.

In the present invention, cubic boron nitride is added in advance as a seed crystal to a molded body or laminated body of the above-mentioned catalyst substance and hexagonal boron nitride, and this is used as a nucleus to promote crystal growth of cubic boron nitride. It is preferable to use the method. In this case, the surface of the seed crystal of cubic boron nitride may be coated with the above catalyst substance. A molded body of the above-mentioned catalyst substance and hexagonal boron nitride or the like is filled in a reaction vessel and loaded into a well-known high temperature and high pressure generator, under a temperature and pressure condition within a thermodynamically stable region of cubic boron nitride. Hold on. Regarding this thermodynamic stable region, O. Fukunaga, D
iamond Relat. Mater. , 9 (20
00), 7-12, generally in the range of about 4 to about 6 GPa, about 1400 to about 1600 ° C,
The holding time is generally about 1 second to about 6 hours. By holding in the thermodynamically stable region of the cubic boron nitride described above, the hexagonal boron nitride is converted to cubic boron nitride, which is generally composed of hexagonal boron nitride, cubic boron nitride and a catalytic material. A lump is obtained. This synthetic mass is crushed and cubic boron nitride is isolated and purified.

The isolation and purification method is described in JP-B-49-277.
The method described in Japanese Patent No. 57 can be used. For example, after crushing the synthetic mass to 5 mm or less, add sodium hydroxide and a small amount of water and heat to about 300 ° C.
Hexagonal boron nitride is selectively dissolved. After cooling, washing with acid, washing with water, and filtration, the cubic boron nitride abrasive grains are recovered.

Among the cubic boron nitride abrasive grains thus obtained, those suitable for the present invention are the abrasive grains substantially made of single crystal. Cubic boron nitride abrasive grains, in addition to single crystalline crystals, include cubic boron nitride abrasive grains such as polycrystalline or fine crystalline, in the present invention, among them, single crystalline crystals Is preferably used. Polycrystalline or fine crystalline cubic boron nitride abrasive grains have a relatively high abrasive grain strength and are difficult to chip, so when used as a grindstone, the cutting edge of the abrasive grains is easily worn away, and the cubic crystal of the present invention is used. Not suitable for boron nitride abrasives. Therefore, the concept of the abrasive grains that are substantially single crystal in the present invention does not include polycrystalline and fine crystalline.

The definition of "substantially single crystalline" in the present invention is that the above-mentioned abrasive grains are 90% by volume or more, preferably 95% by volume or more, more preferably 99% by volume or more in the cubic boron nitride abrasive grains. Is present in the ratio of. Note that this ratio does not include impurities other than cubic boron nitride.

The cubic boron nitride abrasive particles obtained as described above are classified into particle size categories specified in JIS-B4130, and then the blocky abrasive particles are removed using a shape separator or the like for each particle size category to obtain It is possible to obtain cubic boron nitride abrasive grains satisfying the filling rate of the invention.

The term "blocky abrasive grains" means that the crystal grains have a shape close to a sphere. Specifically, when the triaxial major axis of the crystal grains is L (μm) and the thickness is T (μm). , L / T
Indicates an abrasive grain having a value of 1 close to 1. The triaxial diameter referred to here is a method of quantifying the particle shape by converting irregularly shaped particles into a rectangular parallelepiped. See the Powder Engineering Handbook, Powder Engineering Handbook, page 1 of the 1st edition of 1986, 1st edition. There is a description.

Specifically, parallel lines are brought close to each other from both sides with respect to a projected figure of a particle stably arranged on an arbitrary plane on the plane, and an interval between the parallel lines when the projected figure is contacted is measured. . The distance between parallel lines where this distance is the longest is the major axis L of the grain.
(Μm), and the distance between parallel lines contacting the projected figure in the direction perpendicular thereto is defined as the particle minor axis B (μm). The height from the surface where the particles are stably arranged to the upper end of the particle is defined as the thickness T of the particle.
(Μm). However, the thickness T (μ
m), the minor axis B (μm) of the grain and the thickness T (μ
The thickness of the smaller one of m) is T (μm).

That is, in the present invention, by using a shape separator or the like, the ratio of the abrasive grains having L / T of 1.5 or less is reduced, so that the cubic boron nitride abrasive grains satisfying the filling rate of the present invention can be obtained. Obtainable. In the manufacturing method of the present invention, "removing abrasive grains having L / T of 1.5 or less" means "L / T
The step of reducing the ratio of abrasive grains having T of 1.5 or less ”.

As the shape separator, any shape separator can be used as long as it achieves the above-mentioned purpose. For example, a method of separating abrasive grains having a low L / T by vibration can be mentioned. An example of a concrete structure of the shape separator by this method is an equilateral triangular vibration plate (each vertex is A, B, C,
The edges AB are provided on the sides AB and AC to prevent the abrasive grains from falling off), but the diaphragm is tilted so that the vertex B is on the axis of the sides AC. The tilt angle is preferably in the range of 1 to 45 ° with respect to the horizontal. Further, it is inclined from the vertex A toward the vertex C so as to form a depression angle. The depression angle at this time is preferably within the range of 1 to 30 with respect to the horizontal.

While vibrating the plate, the abrasive grains are supplied to the apex A and discharged from the side BC. The supplied abrasive grains flow from the apex A toward the side BC due to vibration. In the process, a blocky abrasive grain with a shape closer to a sphere will roll down to a lower place, and edge A
It flows near C. On the other hand, abrasive grains having irregular shapes (abrasive grains that are not blocky) climb to a high slope due to vibration, and are discharged from the side BC near B.
By dividing the outlets of the side BC, it is possible to obtain abrasive grains in which blocky abrasive grains having a nearly spherical shape are separated. JIS-
Table 1 shows the particle size classifications related to the present invention among the particle size classifications specified in B4130 “Diamond and cubic boron nitride and particle size”. In addition, Table 1 shows a particle size distribution by an electro-sieve.

In order to increase the yield of the cubic boron nitride abrasive grains satisfying the filling rate of the present invention, a step of pulverizing the cubic boron nitride abrasive grains should be included in the process of producing the cubic boron nitride abrasive grains. Is preferred. As a specific crushing method, a crushing method of crushing cubic boron nitride abrasive grains is preferable, and specifically, crushing with a roll crusher is preferable.

The crushing method using a roll crusher is a method of sandwiching abrasive grains between two rolls and crushing the abrasive grains. This method is a method of crushing abrasive grains by applying compression and shearing force, and because it is crushed in a short time with a relatively strong force, it becomes finer than necessary and the grains of the abrasive grains become blocky and become blocky. It is possible to improve the yield of cubic boron nitride abrasive grains that satisfy the filling rate of the present invention.

As another method of obtaining cubic boron nitride abrasives satisfying the filling factor of the present invention, a method of converting hexagonal boron nitride into cubic boron nitride in the presence of a catalyst substance under ultrahigh pressure and high temperature conditions, A direct method is to obtain the abrasive grains that satisfy the filling rate of the present invention. Specifically, a mixture containing a hexagonal boron nitride and a seed crystal of cubic boron nitride is kept under a pressure-temperature condition which is thermodynamically stable for the cubic boron nitride. By using twin crystals or multiple twin crystals as seed crystals of cubic boron nitride in the production of grains, cubic boron nitride abrasive grains satisfying the filling rate of the present invention can be obtained.

The twin crystal is a crystal having two parts having a symmetrical relationship with each other. A specific crystal form of a twin crystal is schematically shown in FIG. By using a twin crystal as a seed crystal, the reason why the cubic boron nitride abrasive grains satisfying the filling rate of the present invention can be obtained is that the nucleation is one-dimensional in the recessed angle of the twin, that is, one crystal orientation. Since it progresses, a difference in the growth rate is more likely to occur as compared with the crystal growth in other crystal orientations, and the number of crystal grains that grow anisotropically increases. As a result, irregular abrasive grains are easily grown, and cubic boron nitride abrasive grains satisfying the filling rate of the present invention are easily obtained.

For example, in a twin crystal as shown in FIG. 1 (A), growth in the directions of three arrows occurs preferentially. Moreover, when a multiple twin crystal having two or more twin planes as shown in FIG. 1 (B) is used as a seed crystal, the number of planes having a recessed angle increases, and the crystal as shown in FIG. 1 (A) is used. The cubic boron nitride abrasive grains satisfying the filling rate of the present invention are more likely to grow than in the case of the above. When a grindstone is produced using the cubic boron nitride abrasive grains of the present invention, a high grinding ratio and sharpness can be obtained. This effect is particularly remarkable in the case of a vitrified bond grindstone having pores.

The abrasive grain ratio in the vitrified bond grindstone is ((filling ratio of cubic boron nitride abrasive grains−0.1) × 1
00) volume% ~ ((cubic boron nitride abrasive grain filling rate +
0.05) × 100)% by volume, and in particular, the abrasive grain ratio in the vitrified bond grindstone is ((packing ratio of cubic boron nitride abrasive grains−0.05) ×
100)% by volume to ((filling rate of cubic boron nitride abrasive grains +
It is preferably within the range of 0.05) × 100) volume%. If the abrasive grain ratio is smaller than ((cubic crystal boron nitride abrasive grain filling rate−0.1) × 100) volume%, bridges between the abrasive grains are not sufficiently formed, and the retention force of the abrasive grains is sufficient. Since it cannot be obtained, the grinding ratio is reduced. On the other hand, the abrasive grain ratio is ((cubic crystal boron nitride abrasive grain filling ratio +0.05) x
If it is larger than 100% by volume, a bridge between the abrasive grains can be sufficiently obtained, but the abrasive grains are forced to be pressed at the time of forming the grindstone, and the edges of the abrasive grains are chipped or the abrasive grains themselves are crushed. Since these broken or broken abrasive grains fall off during grinding, the grinding ratio decreases.

The abrasive grain ratio is the percentage of the abrasive grain volume in the grindstone volume.

As the binder for the vitrified bond grindstone, a binder usually used for cubic boron nitride abrasive grains can be used according to the purpose of use. Examples of the binder include those based on SiO ₂ and Al ₂ O ₃ . Further, the compounding amount of the binder in the grindstone is 10 to 3
It is preferably within the range of 0% by volume. When the compounding amount of the binder is less than 10% by volume, the holding force of the abrasive grains is reduced, and as a result, the abrasive grains are more likely to fall off and the grinding ratio is reduced, which is unsuitable as a grinding tool. On the other hand, when the compounding amount of the binder exceeds 30% by volume, the grindstone has reduced porosity and reduced sharpness, and the volume expansion during foaming of the grindstone (foaming phenomenon)
Is likely to occur, which is not preferable.

In addition, additives such as aggregates, auxiliary binders and the like which are usually used in producing a grindstone using cubic boron nitride abrasive grains can be used.

The cubic boron nitride abrasive grains of the present invention are suitable for use in not only the above-mentioned vitrified bond grindstone but also grindstones using other kinds of bonds, polishing cloth paper and the like. Abrasive cloth paper is one in which abrasive particles are fixed to a cloth with an adhesive, and specifically, it is fixed to cotton or a cloth similar thereto by using glue, gelatin, synthetic resin or the like as an adhesive. It is manufactured by

[0047]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

(Example 1) hBN (U manufactured by Showa Denko KK)
HP-1, average particle size 8-10 microns, purity 98%) 1
1 part of cBN synthesis catalyst LiCaBN ₂ with respect to 00 parts by mass
0.5 parts by mass of cubic boron nitride abrasive grains having a mean grain size of 30 microns and a large amount of twin crystals shown in FIG. 1 as seed crystals.
A mass part was added and a sample was molded. The molding density of the sample is 1.
It was 92 g / cm ³ . The molded sample was filled in a reaction vessel and loaded in a high temperature and high pressure generator, and then 5 GPa, 1500
Synthesis was carried out by holding at 15 ° C for 15 minutes. After the synthesis, the synthetic lump was taken out of the apparatus, crushed into 5 mm or less, sodium hydroxide and a small amount of water were added, and the mixture was heated to about 300 ° C. to selectively dissolve hexagonal boron nitride. After cooling, this was washed with acid, washed with water, and filtered to isolate and purify yellow and transparent cubic boron nitride abrasive grains. The obtained cubic boron nitride abrasive grains were cubic boron nitride abrasive grains with a single crystal quality of 99% or more.

(Example 2) A cubic boron nitride abrasive grain was prepared in the same manner as in Example 1 except that the seed crystal of cubic boron nitride was not added and the other conditions were the same as in Example 1. It was isolated and purified. The obtained cubic boron nitride abrasive grains were cubic boron nitride abrasive grains with a single crystal quality of 99% or more.

(Example 3) The cubic boron nitride abrasive grains obtained in Example 1 were classified into the grain size categories specified in JIS-B4130.
After washing with dilute hydrochloric acid, deoxidizing and drying, the bulk density was measured to determine the filling rate.

The bulk specific gravity was measured by closing the outlet of the funnel with a stopper and adding 20.0 ± 0.1 g of cubic boron nitride abrasive grains.
Was placed in the funnel. A cylinder having a volume of 8.0 ± 0.1 ml was arranged immediately below the funnel outlet, and the dropping distance from the funnel outlet to the upper surface of the cylinder was 95.0 ± 1.0 mm. After pulling out the stopper and dropping the whole amount of the cubic boron nitride abrasive grains into the cylinder, the cubic boron nitride abrasive grains rising from the upper surface of the cylinder were removed by scooping using a metal plate. Next, the mass of the cubic boron nitride abrasive particles remaining in the cylinder was measured and divided by the cylinder volume to obtain the bulk specific gravity. Table 2 shows the filling rate of the abrasive grains in the grain size classification 100/120.

(Example 4) The cubic boron nitride abrasive grains obtained in Example 2 were classified into the grain size categories defined in JIS-B4130.
The blocky abrasive grains were removed using the shape separator described above.

As the shape separator, a shape separator using an equilateral triangular diaphragm having a side length of about 1 meter was used. The vibrating plate (each vertex is A, B, C) has a vertex B with the side AC as an axis.
Is tilted 13 ° so that
It was tilted by 7 ° so that it became a depression angle.

Using this shape separator, the ratio of the abrasive grains having an L / T of 1.5 or less contained in the cubic boron nitride abrasive grains was reduced, and then the cubic boron nitride abrasive grains were removed. After washing with dilute hydrochloric acid, deoxidizing and drying, the bulk specific gravity was measured by the same method as in Example 3 to obtain the filling rate. Grain size classification 100/12
Table 2 shows the filling rate of the abrasive grains of No. 0.

(Example 5) The cubic boron nitride abrasive grains obtained in Example 2 were pulverized by a roll pulverizer.

A roll crusher manufactured by Yoshida Seisakusho was used as the roll crusher. The roll has a diameter of 140 mm and a length of 1.
40mm hardened steel roll with 50kgf
(490 N) was added, and cubic boron nitride abrasive grains were supplied at 20 g / min to a roll having a rotation speed of 100 rpm for pulverization.

After pulverizing the cubic boron nitride abrasive grains, JIS-
Classified into the particle size classification specified in B4130, and the particle size classification 1
Abrasive grains of 00/120 were washed with dilute hydrochloric acid and deoxidized.
After drying, the bulk density was determined by measuring the bulk specific gravity in the same manner as in Example 3. Table 2 shows the filling rate of the abrasive grains in the grain size classification 100/120.

Example 6 The cubic boron nitride abrasive grains obtained in Example 2 were ground under the same conditions as in Example 5. After crushing the cubic boron nitride abrasive grains, the particles were classified into the particle size classifications defined in JIS-B4130, and the L / T values of the abrasive particles of the particle size classifications 100/120 were measured using a shape separator under the same conditions as in Example 4. After reducing the ratio of abrasive grains of 1.5 or less, washing with dilute hydrochloric acid, deoxidizing and drying, the bulk specific gravity was measured by the same method as in Example 3 to obtain the filling rate. Grain size classification 100/120
Table 2 shows the filling rate of the abrasive grains.

(Comparative Example 1) The cubic boron nitride abrasive grains obtained in Example 2 were classified into the grain size categories specified in JIS-B4130, and the abrasive grains in the grain size category 100/120 were washed with dilute hydrochloric acid and removed. After acid and drying, the bulk specific gravity was measured by the same method as in Example 3 to obtain the filling rate. Grain size classification 100 /
The filling rate of 120 abrasive grains is shown in Table 2.

(Examples 7 and 8, Comparative Examples 2 to 6) Example 3
And a grindstone segment was produced using the abrasive grains of Comparative Example 1. Abrasive grains, borosilicate glassy binder as a binder,
Prepare a mixture of binders (phenolic resins), 1
After pressure molding at 50 ° C, firing was performed at 1000 ° C (atmosphere atmosphere). The binder used burned during firing of the grindstone and became pores. Table 3 shows the abrasive grains used, the compounding ratio, the porosity and abrasive grain ratio after firing of the stone, and the transverse rupture strength of the segment of the thus obtained stone segment.

(Examples 9, 10 and Comparative Examples 7 to 11) The grindstone segments prepared in Examples 7 and 8 and Comparative Examples 2 to 6 were adhered to an aluminum base metal to be grinded, and then the following grinding was performed. A grinding test was performed under the conditions. The grinding results are shown in Table 4.

[0062]   Whetstone 1A1 type, 150D x 10U x 3X x 76.2H   Grinding machine Horizontal axis surface grinding machine (3.7 kW whetstone axis motor)   Work Material SKH-51 (HRc = 62-64)                   Work material surface 200 mm x 100 mm   Grinding method Wet surface traverse grinding method   Grinding condition Wheel speed 1800m / min                   Table speed 15m / min                   Cross feed 5mm / pass                   Notch 25 μm Grinding fluid JIS W2 class cBN dedicated fluid (50 times dilution)

[0063]

[Table 1]

[0064]

[Table 2]

[0065]

[Table 3]

[0066]

[Table 4]

[0067]

The cubic boron nitride abrasive grains of the present invention have a filling rate lower than that of conventional cubic boron nitride abrasive grains, and have a characteristic that a bridge between the abrasive grains can be maintained even if the abrasive grain ratio is reduced. Therefore, a grindstone using the cubic boron nitride abrasive grains of the present invention,
High grindstone hardness, high transverse rupture strength, and high grain retention were obtained even with high porosity. Furthermore, by using the cubic boron nitride abrasive grains of the present invention, it becomes possible to manufacture a grindstone having good sharpness without lowering the grinding ratio of the grindstone.

In particular, the cubic boron nitride abrasive grain of the present invention is suitable for a vitrified bond grindstone, and the vitrified bond grindstone using the cubic boron nitride abrasive grain of the present invention has excellent grinding characteristics as a pored grindstone.

[0069]

[Brief description of drawings]

FIG. 1A shows twin crystals of cubic boron nitride. The arrow indicates the direction of preferential growth. (B) shows multiple twin crystals of cubic boron nitride. The arrow indicates the direction of preferential growth.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C01B 21/06 C01B 21/06 N (72) Inventor Takuya Okubo 1-sect Suga, Shiojiri City, Nagano Showa Denko KK In-house Shiojiri Production and Technology Management Department (72) Inventor Makoto Kasahara No. 1 Soga, Shiojiri City, Nagano Prefecture Showa Denko Co. Electric Works Co., Ltd. Shiojiri Production / Technology Division F Term (Reference) 3C063 AA02 AB03 AB07 BA03 BB02 BC05 BG15 BH07 CC02 FF23 FF30

Claims (13)

[Claims] 1. A cubic boron nitride abrasive by holding a mixture containing hexagonal boron nitride and cubic boron nitride seed crystals under pressure temperature conditions which are thermodynamically stable for cubic boron nitride. In the method for producing grains, a method for producing cubic boron nitride abrasive grains, wherein the seed crystal of cubic boron nitride includes twin crystals of cubic boron nitride. 2. A method for producing a cubic boron nitride abrasive grain, comprising pulverizing the cubic boron nitride abrasive grain produced by the method for producing a cubic boron nitride abrasive grain according to claim 1. 3. The method for producing cubic boron nitride abrasive grains according to claim 2, wherein a roll pulverizer is used for pulverizing the cubic boron nitride abrasive grains. 4. From the cubic boron nitride abrasive grain produced by the method according to claim 1, the cubic boron nitride abrasive grain has a triaxial major axis of L (μm) and a thickness of T (μ
A method for producing cubic boron nitride abrasive grains, characterized in that the abrasive grains having L / T of 1.5 or less are removed. 5. A cubic boron nitride abrasive produced by the method for producing a cubic boron nitride abrasive according to any one of claims 1 to 4. 6. The cubic boron nitride abrasive grains, the bulk specific gravity (unit: g / cm ³⁾ the cubic is calculated by dividing the true density of cubic boron nitride (3.48 g / cm ³⁾ crystal The filling rate of boron nitride abrasive grains is a particle size classification defined in JIS-B4130. In the case of 40/50 abrasive grains, it is within the range of 0.482 to 0.282, and in the case of 50/60 abrasive grains, it is 0.480. Within the range of 0.280, within the range of 0.478 to 0.278 for the 60/80 abrasive grains, within the range of 0.474 to 0.274 for the 80/100 abrasive grains, within the range of 100/120. Abrasive grains 0.469-0.2
In the range of 69, 120/140 abrasive grains, 0.464
In the range of ~ 0.264, 140/170 abrasive grains,
In the range of 0.459 to 0.259, in the case of 170/200 abrasive grains, in the range of 0.453 to 0.253, 200/2
In the case of 30 abrasive grains, within the range of 0.446 to 0.246, 2
Within the range of 0.440 to 0.240 for the 30/270 abrasive grains, 0.433 to 0.2 for the 270/325 abrasive grains.
Within the range of 33, 0.426 with 325/400 abrasive grains
A cubic boron nitride abrasive grain characterized by being in the range of ˜0.226. 7. The cubic boron nitride abrasive grain according to claim 6, wherein the cubic boron nitride abrasive grain is substantially single crystalline. 8. A grindstone produced using the cubic boron nitride abrasive grains according to claim 5 and a binder. 9. The grindstone according to claim 8, wherein a vitrified bond is used as the bonding material. 10. The grindstone according to claim 9, wherein the compounding amount of the vitrified bond in the grindstone is within a range of 10 to 30% by volume. 11. An abrasive grain ratio in a grindstone is ((filling ratio of cubic boron nitride abrasive grains−0.1) × 100) volume% to ((filling ratio of cubic boron nitride abrasive grains + 0.05). It is in the range of x100) volume%, The grindstone in any one of Claims 8-10 characterized by the above-mentioned. 12. An abrasive grain ratio in a grindstone is ((filling ratio of cubic boron nitride abrasive grains−0.05) × 100) volume% to ((filling ratio of cubic boron nitride abrasive grains + 0.05). It is in the range of x100) volume%, The grindstone in any one of Claims 8-10 characterized by the above-mentioned. 13. A polishing cloth paper produced by fixing the cubic boron nitride abrasive grains according to any one of claims 5 to 7 to a cotton cloth or a cloth equivalent thereto with an adhesive.