JPH11209745A - Grinder composition for grinding glass and grinding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject composition capable of forming a ground surface having a high accuracy on a glass base plate for a magnetic disc by containing a basic salt of magnesium. SOLUTION: This grinding composition for grinding a glass is obtained by containing (A) a basic salt of magnesium selected from magnesium hydroxide, magnesium carbonate, basic magnesium carbonate [3MgCO3 .Mg(OH)2 ], or the like. In order to make the component (A) itself contribute to the grinding in a powdery state, a preferable particle size is regulated to 0.1-10 μm as a mean particle diameter. The adding amount of the component (A) is preferably 1-40 wt.%, more preferably 5-30 wt.% as a solid portion concentration in a slurry. As a method for using the composition, it is preferable to grind the plate by using the composition after grinding roughly with a grinding material consisting of one or more kinds selected from cerium oxide, zirconium oxide, iron oxide and silicon dioxide as the main components.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an abrasive composition for glass polishing, and more particularly to an abrasive composition for glass polishing capable of forming an excellent polished surface without defects.
In particular, the present invention relates to an abrasive composition for polishing a glass for a magnetic disk, which can be polished to a high-precision mirror surface suitable for a magnetic head to fly with a low flying height, and a polishing method thereof.

[0002]

2. Description of the Related Art As a substrate for a magnetic disk used as a storage medium for a personal computer or the like incorporated in a drive device, it has higher shock resistance and higher smoothness than an aluminum substrate. Glass substrates are used. Recently, due to the demand for higher recording density, the distance between the magnetic head and the magnetic disk substrate has been getting smaller and smaller, and the glass substrate for the magnetic disk has a higher precision flatness, smaller surface roughness and less defects. Things are in great demand. Materials such as cerium oxide, zirconium oxide, iron oxide, and silicon dioxide have been used for various types of glass polishing for a long time. At present, an abrasive composition containing cerium oxide as a main component (hereinafter referred to as “cerium oxide-based abrasive composition”) is mainly used because of its high polishing efficiency.

An abrasive composition for a glass substrate for a magnetic disk has improved polishing efficiency and polishing accuracy by adjusting the slurry characteristics by adding an additive to an abrasive mainly composed of cerium oxide, zirconium oxide and aluminum oxide. There are the following technologies for the purpose of causing the following. JP-A-3-146584 "Abrasive for glass polishing" A material mainly containing zirconium oxide containing calcium aluminate, magnesium sulfate and magnesium chloride JP-A-3-146585 "Abrasive for glass polishing" Mainly cerium oxide JP-A-9-109020 "Magnetic disk polishing composition and polishing liquid using the same" Japanese Patent Application Laid-open No. 9-109020 "A magnetic disk polishing composition containing gibbsite and a dispersant in an aluminum oxide-based component" For glass substrates for use, the surface accuracy is increasing more and more as the day progresses. In order to stably maintain the low flying height required as a characteristic of a glass substrate for a magnetic disk, a conventional abrasive composition must have a surface roughness and a clean glass surface free of deposits necessary for the abrasive composition. Can not.

[0004]

As described above, in order to increase the recording density of a magnetic disk, it is essential to reduce the flying height of a magnetic head. Are becoming more stringent. Even if the crystallized glass or tempered glass substrate used for the magnetic disk glass substrate is polished using the conventionally used cerium oxide-based abrasive composition, the flying height of the magnetic head is required There is a problem that the required surface roughness cannot be obtained because the surface roughness is lowered.
In addition, since the cerium oxide-based abrasive composition has a high chemical reactivity with glass, deposits remain on the surface of the glass substrate for a magnetic disk, and mechanical energy such as ultrasonic cleaning or scrub cleaning is applied. However, it is difficult to completely remove the deposits, and the magnetic head comes into contact with the remaining deposits.Therefore, it is difficult to obtain a high-precision magnetic disk surface suitable for substantially reducing the flying height of the magnetic head. is there.

[0005]

The inventor of the present invention has conducted intensive studies on the most suitable abrasive for obtaining a highly polished surface on a glass substrate for a magnetic disk. As a result, the basic salt of magnesium, especially In particular, by using a glass polishing abrasive composition comprising at least one selected from magnesium hydroxide, magnesium carbonate, basic magnesium carbonate, and various magnesium phosphates, a conventional cerium oxide-based abrasive composition can be achieved. It has been found that a highly accurate polished surface can be obtained. In addition, a glass polished surface obtained by polishing using an abrasive mainly containing at least one of cerium oxide, zirconium oxide, iron oxide and silicon dioxide is used as a basic salt of magnesium, especially, hydroxide. By polishing using an abrasive composition containing at least one selected from magnesium, magnesium carbonate, basic magnesium carbonate and various magnesium phosphates, removal of residual deposits such as cerium oxide-based abrasives can be achieved. This makes it possible to obtain a highly polished glass surface at the same time. As a result, the flying height of the magnetic head, which cannot be achieved conventionally, can be reduced.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific examples of the basic salt of magnesium used in the present invention include magnesium hydroxide, magnesium carbonate and basic magnesium carbonate (3MgCO3).
₃ , Mg (OH) ₂ ) and various magnesium phosphates such as magnesium phosphate and magnesium hydrogen phosphate, but the present invention is not limited thereto. In the present invention, the purity of these compounds is not particularly limited. Since the basic salt of magnesium used in the present invention itself contributes to polishing in a powder state, the preferred particle size is 0.1 to 10 μm as an average particle size. If it exceeds 10 μm, sedimentation in the slurry becomes remarkable and not only poses a problem in work, but also the required polishing surface roughness may not be obtained in some cases. .

The amount of the basic magnesium salt used in the present invention is 1 to 40 wt.% As the solid content concentration in the slurry (when two or more basic salts of magnesium are used). %, More preferably 5 to 30 wt. %. 1 wt. %, It is difficult to obtain a highly accurate surface, and surface defects are liable to occur. Also, 40w
t. %, It is difficult to obtain a further improvement effect by increasing the amount. When one or more basic salts of magnesium are mixed, their mixing ratio can be arbitrarily selected. In addition, the basic salt of magnesium used in the present invention has the same chemical formula excluding water of crystallization, the number of water of crystallization is different, or the crystal system is different, the appearance is different, the shape is different, It is not particularly limited to them. The solvent of the abrasive composition of the present invention is not limited to water, but in many cases, an aqueous system is preferred in various respects.

The abrasive composition of the present invention may further contain glycols such as ethylene glycol and polyethylene glycol, tripolyphosphate, hexametaphosphate and the like, if necessary, for further improving dispersibility, preventing sedimentation, improving stability and improving workability. Or a polymer dispersant such as a phosphate or polyacrylate, a cellulose ether such as methylcellulose or carboxymethylcellulose, or a water-soluble polymer such as polyvinyl alcohol. The amount of addition to these abrasives is 0.05 to 20 wt. % Is normal, preferably 0.1 to 15 wt. %, More preferably 0.1 to 10 wt. %.

In order to improve the polishing efficiency of the polishing composition of the present invention, substances having a polishing promoting effect on glass, for example, amino acids such as arginine, amines such as melamine and triethanolamine, cerium fluoride Rare earth fluoride compounds such as citric acid, tartaric acid, malic acid, etc.
An organic acid such as gluconic acid may be added. The method of producing the abrasive composition of the present invention may be any mixture of various raw materials, and is not particularly limited. Preferably, a ball mill,
What is necessary is just to mix and prepare mechanically by the high-speed mixer etc. in the said mixing ratio. The method of using the abrasive composition of the present invention can be performed in the same manner as a normal abrasive composition, but a more preferred polishing method is at least one of cerium oxide, zirconium oxide, iron oxide and silicon dioxide. After rough polishing with an abrasive mainly composed of, a basic salt of magnesium, especially, from various magnesium phosphates such as magnesium hydroxide, magnesium carbonate, basic magnesium carbonate, magnesium phosphate, magnesium hydrogen phosphate, etc. Polishing is performed using an abrasive composition containing at least one or more selected basic salts of magnesium, whereby highly accurate polishing which has not been achieved in the past can be efficiently performed.

The object to be polished after polishing is usually subjected to ultrasonic cleaning in pure water, optionally with the addition of a surfactant. Further, for easy washing, a diluted aqueous solution for a strong acid such as hydrochloric acid, sulfuric acid, nitric acid, etc., a weak acid or a slightly diluted aqueous solution, and an aqueous solution of an ammonium salt for magnesium hydroxide. It is better to use
In the polishing with the abrasive composition of the present invention, there is no residual deposit on the glass surface after washing as described above as compared with the conventional product, and the flying height of the magnetic head is reduced to about 0.25 microinch. Thus, a great effect can be obtained for increasing the density of the glass substrate for a magnetic disk.

[0011]

The present invention will be described below in detail based on examples and comparative examples. Examples are given of magnesium hydroxide and magnesium carbonate as specific examples of the basic salt of magnesium, but the present invention is not limited to these.

Examples 1 to 14 Classification was performed using magnesium hydroxide (Kyowa Suimag F, average particle diameter d ₅₀ = 4 μm) manufactured by Kyowa Chemical Industry Co., Ltd. as a raw material.
Coarse particles were removed to produce a particle having an average particle diameter d ₅₀ = 3.5 μm (referred to as “magnesium hydroxide A”). The raw material magnesium hydroxide was pulverized and classified to produce fine particles (average particle diameter d ₅₀ = 0.5 μm) (referred to as “magnesium hydroxide B”). Also, magnesium carbonate is
Manufactured by Kyowa Chemical Industry Co., Ltd. (average particle diameter d ₅₀ = 1.0 μm)
m, for filler), and then classified to obtain an average particle diameter d ₅₀ =
Fine granules of 0.5 μm were made.

Using a high-speed mixer under the conditions shown in Table 1, pure water dispersion-based abrasive compositions Examples 1 to 14 were produced. At this time, a polyacrylic acid-based dispersant (Poise 530, manufactured by Kao Corporation) was added to all the powders for 1 w
t. % Was added. As a work piece, a crystallized glass substrate mainly composed of 2.5 inch lithium silicate ((crystal phase of lithium silicate and cristobalite) polished in advance with a cerium oxide-based abrasive (ROXH-1 manufactured by Tohoku Metal Chemical Co., Ltd.) And an amorphous phase) R _a = 1
0 °, R _max = 250 °)
And ) Or a tempered glass substrate mainly composed of aluminosilicate (R _a = 9 °, R _max = 180 °) (Table 1)
"Work B". ) Was polished under the following conditions.

Polishing machine: 4-way type double-side polishing machine (Fujikoshi Kikai Kogyo Co., Ltd., 5B type) Polishing pad: Suede type (Chiyoda Co., Ltd., Shigaru 1900W) Slurry supply speed: 60 ml / min Lower platen rotation speed : 45 rpm Processing pressure: 75 g / cm ² Polishing time: 7 min

The polished glass disk was taken out of the polishing machine, subjected to ultrasonic cleaning with pure water, and then subjected to ultrasonic cleaning in a dilute nitric acid aqueous solution (1 wt.% Concentration) bath. Thereafter, the substrate was washed with pure water, dried, and evaluated as follows. (I) Disk surface roughness: _Ra , _Rmax Surface roughness _Ra and R using an atomic force microscope (AFM)
_{The max} was measured. (Ii) Disk surface defects Surface defects were observed for adhesion, pits and scratches using a differential interference microscope, and evaluated by a three-level system of ○: good, Δ: normal, ×: poor. (iii) Head flying height: GA (glide avalanche) A magnetic film is applied to a polished disk, and the head flying height G
A was measured. Specifically, by the sputtering method,
At a substrate temperature of 200 ° C., a ₆₀ nm Cr as a base layer, a 20 nm Co ₁₃ Cr ₆ Pt ₃ Ta alloy as a magnetic layer, and a 10 nm carbon as a protective layer are successively formed.
The magnetic recording medium created by applying a system lubricant is applied to a Glide Height Tester (manufactured by Sony Tektronix).
A was measured. Table 1 shows the results. The average particle size of the abrasive was Granul manufactured by Cilas.
It is a value measured by an instrument HR850.

Comparative Examples 1-2 As a comparative example, the above-mentioned glass substrate polished in advance was replaced with a basic cerium oxide abrasive (RO, manufactured by Tohoku Metal Chemical Co., Ltd.) in place of the basic salt of magnesium used in the present invention.
XF620). Polishing was performed using a% aqueous dispersion slurry and evaluated. These conditions are the same as those described in the above embodiment.

As can be seen from the results of Examples and Comparative Examples,
In any of the examples, excellent results were obtained in any of the surface roughness, the surface defect, and the glide avalanche. The glide avalanche obtained here is a low value that cannot be obtained with a conventional abrasive.

[0018]

[Table 1]

[0019]

According to the present invention, a surface accuracy which cannot be obtained with the conventional abrasive composition can be obtained, and in the case of a glass substrate for a magnetic disk, the flying height of the magnetic head can be further reduced, The present invention is an extremely useful abrasive composition, which greatly contributes to increasing the density of a hard disk.

Continued on the front page (72) Inventor Yutaka Yamauchi 5-1 Yawata Kaigandori, Ichihara-shi, Chiba Prefecture Showa Denko Corporation HD Factory

Claims (3)

[Claims] An abrasive composition for polishing glass, comprising a basic salt of magnesium. 2. The method according to claim 1, wherein the basic salt of magnesium is magnesium hydroxide, magnesium carbonate, basic magnesium carbonate,
2. The composition according to claim 1, wherein the composition is at least one selected from various magnesium phosphates. 3. The glass polishing abrasive composition according to claim 1, wherein the glass polished with an abrasive mainly containing at least one of cerium oxide, zirconium oxide, iron oxide and silicon dioxide is used. A glass polishing method characterized in that polishing is performed by using.