JP2012038361A - Cerium oxide-based polishing agent and method for manufacturing hard disk substrate made of glass - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cerium oxide-based polishing agent substantially free of fluorine that can polish a glass substrate used for a hard disk substrate at high polishing speed, while achieving the reduction of surface roughness of glass substrate and the suppression of the occurrence of polishing flaws, and to provide a method for manufacturing a hard disk substrate made of glass.SOLUTION: There are provided a cerium oxide-based polishing agent for a hard disk substrate made of glass that satisfies the following requirements (1) to (5); and a method for manufacturing the hard disk substrate made of glass using the polishing agent. (1) The cerium oxide-based polishing agent has the total amount of rare earth oxides (TREO) of 95 mass% or more, and the amount of cerium oxide of 99 mass% or more based on the TREO. (2) The cerium oxide-based polishing agent contains fluorine of 0.05 mass% or less. (3) The cerium oxide has the crystallite diameter of 700 to 1000 Å calculated from powder X-ray diffraction. (4) The cerium oxide has the average particle diameter (D) of 0.4 to 0.8 μm. and (5) The hard disk substrate made of glass has the Vickers hardness of 570 Hv or more.

Description

  The present invention relates to a method for producing a cerium oxide-based abrasive and a glass hard disk substrate.

  In recent years, glass materials have been used for various purposes. In particular, high surface precision and low defects are required for glass substrates for hard disks, glass substrates for liquid crystals, glass substrates for LSI photomasks, etc., and therefore, it is common to perform precise surface polishing.

For polishing the surface of a glass substrate, it is common to use a composite rare earth oxide polishing material mainly containing cerium oxide and containing lanthanum oxide, praseodymium oxide, neodymium oxide and the like. This composite rare earth oxide abrasive is pulverized, fired, classified, etc., by refining ore such as bust nesite or monazite ore containing cerium compounds, lanthanum compounds, praseodymium compounds, neodymium compounds, metal oxides, etc. It is obtained through this process. Therefore, impurities such as metal oxides originating from the raw material remain in the composite rare earth oxide abrasive.
Here, the ratio of the pure rare earth oxide compound (cerium oxide + lanthanum oxide + praseodymium oxide + neodymium oxide) contained in the composite rare earth oxide abrasive is referred to as TREO (Total Rare Earth Oxide).

  In general, a composite rare earth oxide abrasive having a high TREO can obtain a higher polishing rate. This is because a mechanical property depending on the hardness of the composite rare earth oxide abrasive particles when a glass substrate is polished with the composite rare earth oxide abrasive. It is considered that the polishing process proceeds efficiently not only by the effect but also by the combined effect of the chemical effect generated between the cerium oxide and the glass substrate.

  Furthermore, it is known that a higher polishing rate can be obtained by using, for example, a composite rare earth oxide abrasive in which fluorine is allowed to act on the composite rare earth oxide abrasive. The effect of fluorine here is considered to be that the primary crystal size (crystallite diameter) of the composite rare earth oxide abrasive is increased to increase the mechanical force that contributes to polishing. However, fluorine is an environmental load substance specified in the Water Pollution Control Law, and from the environmental aspect, it is required to use an abrasive that does not contain fluorine for future glass substrate polishing.

  Hard disk glass substrates improve mechanical properties, especially hardness and rigidity, to prevent disk shake when rotating at high speeds and to prevent damage when a mobile device with a hard disk is dropped. Etc. are becoming more demanding year by year. In order to satisfy these mechanical property requirements, the chemical composition and manufacturing method of glass are improved year by year. As a result, tempered glass substrates mainly composed of aluminosilicate and crystallized glass substrates mainly composed of lithium silicate have been used for hard disks.

  However, these glass substrates all have poor workability, and the polishing rate becomes extremely slower than that of conventional glass. Therefore, an abrasive having a high polishing rate is required in order not to deteriorate productivity. In particular, in the case of crystallized glass, which has been studied in Patent Document 1, there is a large difference in the polishing rate between the crystal part and the amorphous part, and unevenness due to crystal particles remains on the crystal surface, so that low surface roughness is achieved. It has been difficult to achieve.

Furthermore, the recording density of glass hard disks is increasing year by year, and in order to achieve this, it is necessary to reduce the surface roughness of the glass substrate and shorten the distance between the glass substrate and the magnetic head. Therefore, it is conceivable to reduce the average particle size (D ₅₀ ) of the composite rare earth oxide abrasive in order to reduce the surface roughness, but at the same time, the polishing rate is also lowered and the productivity may be deteriorated. In particular, in a glass substrate with poor workability, which has been increasingly used in recent years, the deterioration of productivity becomes more remarkable. In addition, an abrasive that does not contain fluorine is demanded from the environmental viewpoint. When a composite rare earth oxide abrasive that does not substantially contain fluorine is used, even if TREO is high, the effect due to the presence of fluorine is effective. It cannot be obtained, and the polishing rate is further reduced due to the demerits caused by the small D ₅₀ .

JP 2002-150548 A

The present invention has been made to solve the above-described problems of the prior art.
The object of the present invention is to substantially contain fluorine, which is an environmentally hazardous substance, and to reduce the surface roughness of the glass substrate with poor processability used for the hard disk substrate at a high polishing rate than before, And it is providing the cerium oxide type abrasive | polishing agent which can suppress generation | occurrence | production of an abrasion flaw. Another object of the present invention is to provide a method for efficiently producing a glass hard disk substrate using the cerium oxide-based abrasive of the present invention.

As a result of intensive studies to achieve the above object, the present inventors have determined that the total amount of rare earth oxide (hereinafter sometimes referred to as “TREO”) is 95 mass even if the abrasive material does not substantially contain fluorine. % Or more, the cerium oxide concentration in TREO is 99 mass% or more, the crystallite diameter of X-ray diffraction of cerium oxide is 700 to 1000 mm, and the average particle diameter (D ₅₀ ) of the abrasive is 0.4 to 0.8 μm. By polishing the glass substrate for hard disk substrates with poor processability (high hardness) at a high polishing rate without applying the environmental load caused by the presence of fluorine, it is possible to reduce the surface roughness and generate scratches. It was found that polishing can be carried out with suppression. The present invention has been completed based on such findings. That is, the present invention is as follows.

[1] A cerium oxide-based abrasive for producing a glass hard disk substrate that satisfies the following (1) to (5).
(1) The total rare earth oxide amount (TREO) is 95% by mass or more, and the cerium oxide amount with respect to the TREO is 99% by mass or more.
(2) The fluorine content is 0.05% by mass or less.
(3) The crystallite diameter of the cerium oxide calculated from powder X-ray diffraction is 700 to 1000 mm.
(4) The average particle diameter (D ₅₀ ) is 0.4 to 0.8 μm.
(5) The glass hard disk substrate has a Vickers hardness of 570 Hv or more.

[2] The cerium oxide-based abrasive according to [1], wherein the glass hard disk substrate has a Vickers hardness of 600 Hv or more.
[3] The cerium oxide-based abrasive according to [2], wherein the glass hard disk substrate has a Vickers hardness of 620 Hv or more.
[4] The cerium oxide abrasive according to [3], wherein an average crystal size of crystals contained in the glass hard disk substrate is 20 nm or less.

[5] A method for producing a glass hard disk substrate, comprising a polishing step of polishing a glass substrate having a Vickers hardness of 570 Hv or more with the polishing cloth while supplying the polishing material according to [1] to the polishing cloth.
[6] The method for producing a glass hard disk substrate according to [5], wherein the glass substrate has a Vickers hardness of 600 Hv or more.
[7] The method for producing a glass hard disk substrate according to [6], wherein the glass substrate has a Vickers hardness of 620 Hv or more.
[8] The method for producing a glass hard disk substrate according to [7], wherein an average crystal size of crystals contained in the glass substrate is 20 nm or less.

  According to the present invention, it does not substantially contain fluorine, which is an environmentally hazardous substance, and even on a glass substrate with poor processability used for a hard disk substrate, the surface roughness is reduced compared to the conventional at a high polishing rate, And it is providing the cerium oxide type abrasive | polishing agent which can suppress generation | occurrence | production of an abrasion flaw. Moreover, the manufacturing method which manufactures a glass hard disk board | substrate efficiently can be provided using the cerium oxide type abrasive | polishing agent of the said invention. In particular, in polishing of a substrate including a crystal part and an amorphous part of crystallized glass, a high polishing rate can be maintained while suppressing the surface roughness and the level of polishing flaws as compared with the prior art.

[1. Cerium oxide abrasive]
The cerium oxide type abrasive | polishing agent of this invention is used for manufacture of a glass hard disk board | substrate, and satisfy | fills the requirements of following (1)-(5).

First, the cerium oxide-based abrasive of the present invention has (1) a total rare earth oxide amount (TREO) of 95% by mass or more and a cerium oxide amount with respect to the TREO of 99% by mass or more. When the total amount of rare earth oxide is less than 95% and the cerium oxide with respect to the TREO is less than 99% by mass, a sufficient polishing rate cannot be obtained when polishing a glass substrate for hard disks having poor processability (high hardness).
The total rare earth oxide amount is preferably 97% by mass or more, and more preferably 99% by mass or more. Moreover, it is preferable that the amount of cerium oxide with respect to TREO is 99.5 mass% or more, and it is more preferable that it is 99.9 mass% or more.
The amount of TREO and cerium oxide can be measured by fluorescent X-ray analysis. The “total rare earth oxide” refers to rare earth oxides such as cerium oxide, lanthanum oxide, praseodymium oxide, neodymium oxide and the like.

In the cerium oxide-based abrasive of the present invention, (2) the fluorine content is 0.05% by mass or less, preferably 0.01% by mass or less, and more preferably 0.005% by mass or less. preferable. When fluorine is 0.05% by mass or less, fluorine is not substantially contained, and the burden on the environment can be reduced.
The fluorine content can be measured by absorptiometry.

  In the cerium oxide-based abrasive of the present invention, (3) the crystallite diameter of cerium oxide calculated from powder X-ray diffraction is 700 to 1000 mm, preferably 750 to 950 mm, and preferably 800 to 900 mm. More preferred.

  The crystallite size means the size of a single crystal constituting the abrasive particle. When the crystallite diameter is larger than 1000 mm, scratches are likely to occur during polishing. On the other hand, when the crystallite diameter is smaller than 700 mm, the generation of scratches is suppressed, but the polishing rate of the glass substrate for hard disk becomes too low. End up.

  Here, the abrasive particles constituting the cerium oxide-based abrasive are aggregates of single crystals, and the “crystallite” is a single crystal of cerium oxide or rare earth oxide containing cerium constituting the abrasive particles. is there. In the present invention, “crystallite diameter” refers to the size of the single crystal in the (111) plane direction. The value of the crystallite diameter is measured and calculated as follows, for example, based on a value measured by powder X-ray diffraction analysis which is a general measurement method.

First, X-ray diffraction analysis using Cu—Kα1 line is performed. Thereafter, the full width at half maximum of the maximum peak at 2θ = 10 deg to 70 deg is measured, and the crystallite diameter is calculated by the following Serrer equation:
Dhkl = K × λ / (β × cos θ): Scherrer equation [Dhkl: crystallite diameter (Å, size of crystallite perpendicular to hkl), λ: measured X-ray wavelength (Å), β: crystal Diffraction line broadening by size (radian), θ: Bragg angle of diffraction line (radian), K: Constant (differing between β and D constants)]

In general, it is known that K = 0.9 when a half width β _1/2 is used for β. Also, since the wavelength of the Cu-Kα1 line is 1.54050 mm, the crystallite diameter D in the present invention is calculated based on the following formula:
D = 0.9 × 1.54050 / (β _1/2 × cos θ)

The cerium oxide-based abrasive of the present invention has (4) an average particle diameter (D ₅₀ ) of 0.4 to 0.8 μm, preferably 0.4 to 0.6 μm, and preferably 0.45 to 0.45. More preferably, it is 0.55 μm. When the average particle diameter is less than 0.4 μm, the polishing rate of the glass substrate for hard disk becomes low, and when it exceeds 0.8 μm, scratches (scratches) are likely to occur after polishing.
The average particle diameter is a particle diameter corresponding to a cumulative value of 50% of the volume distribution measured by a laser diffraction type particle size distribution measuring instrument (Microtrack MT-3300 manufactured by Nikkiso Co., Ltd.).

  The Vickers hardness of the glass hard disk substrate produced using the cerium oxide-based abrasive of the present invention is 570 Hv or more, preferably 600 Hv or more, more preferably 620 Hv or more, and 650 HV or more. Is most preferred. According to the cerium oxide type abrasive | polishing agent of this invention, a favorable grinding | polishing characteristic can be exhibited also with respect to the glass substrate of Vickers hardness 570Hv or more considered that conventional workability is bad.

  When the glass hard disk substrate is made of crystallized glass, the average crystal size of the contained crystals is preferably 20 nm or less, and more preferably 3 to 15 μm. When the average crystal size is 20 nm or less, both high substrate strength and small surface roughness after polishing can be achieved. The average crystal size can be calculated by visual measurement from a transmission electron microscope image. In the calculation, 100 or more crystal sizes in an arbitrary direction of the image are measured, and the average value is set as the average crystal size.

  The cerium oxide type abrasive | polishing agent of this invention can be manufactured by improving the manufacturing method of a well-known abrasive | polishing agent suitably. Moreover, it can manufacture also by baking commercially available high purity cerium carbonate. Furthermore, after performing a separation and purification operation from bastonite ore, etc., firing may be performed.

  For example, a rare earth-containing fluorinated carbonate ore bastonite or monazite ore is roasted, dissolved in nitric acid, separated by precipitation, and roasted. The cerium ions are extracted into the organic phase with a solvent such as tributyl phosphate-benzene, and back extracted with an aqueous phase containing a reducing agent such as sodium nitrite to obtain cerium oxalate, followed by firing. It is done.

The firing temperature is appropriately selected depending on the type of cerium carbonate used as a raw material, but is preferably 500 to 1,100 ° C., more preferably 600 to 1,000 ° C. Can be obtained in high yield. In addition, the crystallite diameter can be adjusted by performing firing several times.
The average particle diameter can be adjusted by performing a pulverization treatment before or after firing. Moreover, it is also possible to separate and use those having a desired particle size range by wet classification such as natural classification, filtration with a filter, hydrocyclone, centrifugal settling machine, and centrifugal tilting machine (decanter).

  In the same manner as above, the rare earth complex ore is subjected to various separation and extraction operations and roasting to remove other impurities such as rare earth elements, fluorine, etc., and use high-purity cerium carbonate with increased purity of cerium as a starting material. It can also be mentioned as a more preferable method.

  The cerium oxide type abrasive | polishing agent of this invention can be used with a powder form, For example, it can disperse | distribute to dispersion media, such as water, and can also be used in the state of a slurry about 5-30 mass%. Examples of the dispersion medium in this case include water and water-soluble organic solvents. Examples of the water-soluble organic solvent include alcohol, polyhydric alcohol, acetone, tetrahydrofuran and the like. In general, water is often used.

  A dispersant may be added to the slurry. The dispersant is not particularly limited as long as it is a general dispersant that can impart a dispersing effect to the pulverized slurry. For example, pyrophosphoric acid, sodium pyrophosphate, sodium tripolyphosphate, sodium hexametaphosphate, polystyrene sulfonate (sodium polystyrene sulfonate, potassium polystyrene sulfonate, etc.), polycarboxylate (sodium polyacrylate, sodium polymaleate, etc.), Examples thereof include polyacrylates (sodium polyacrylate, ammonium polyacrylate, etc.), naphthalenesulfonic acid formalin condensates (β-naphthalenesulfonic acid sodium formalin condensates, alkyl naphthalenesulfonic acid sodium formalin condensates, etc.) and the like.

  Moreover, you may add a well-known thickener, a fungicide, an oxidizing agent, a pH adjuster, etc. in the said slurry suitably according to a use.

  Furthermore, it is also possible to add other abrasive grains of 50 mass% or less, preferably 30 mass% or less to the cerium oxide abrasive of the present invention to form a slurry. The other abrasive grains are preferably selected from alumina, silica, zirconia, titania, germania, and the like, among which alumina, silica, zirconia, and the like are particularly preferable.

[2. Manufacturing method of glass hard disk substrate]
The manufacturing method of the glass hard disk substrate of the present invention includes a polishing step of polishing the glass substrate with the polishing cloth while supplying the polishing material of the present invention described above to the polishing cloth. By using the abrasive of the present invention, a glass hard disk substrate having a desired surface roughness (for example, Ra: 2.0 to 5.0 mm) can be efficiently produced.

  Specifically, the glass substrate for a hard disk substrate is polished using the polishing cloth while supplying the polishing agent of the present invention to a polishing cloth of a polishing apparatus such as a single-side polishing machine or a double-side polishing machine. At this time, the abrasive is supplied in the form of a slurry. The polishing step using this abrasive slurry can be performed according to a conventional method. For example, a glass substrate to be polished is held between an upper surface plate and a lower surface plate to which a non-woven fabric or foamed polyurethane polishing pad (polishing cloth) is attached, and polishing is performed between the polishing pad and the substrate. Polishing while supplying the agent slurry. In other words, polishing is performed by rotating and sliding the surface plate while applying a predetermined pressure to bring the polishing agent into close contact with the substrate with the polishing pad. It is considered that the abrasive slurry thus supplied is carried on the polishing pad and polished.

Here, the polishing pressure is preferably from 30 to 150 g / cm ^2, more preferably 50~140g / cm ^2. The platen rotation speed is preferably 10 to 80 rpm, more preferably about 30 to 60 rpm. The polishing time is appropriately set, but is preferably 20 to 60 minutes, and more preferably 30 to 50 minutes.

  In addition, the glass substrate used in the process has a Vickers hardness of preferably 600 Hv or more, more preferably 620 Hv or more, and 650 HV or more from the viewpoint of producing a glass hard disk substrate having excellent mechanical properties. Is most preferred. Moreover, it is preferable that the average crystal size of the crystal | crystallization contained in a glass substrate is 20 nm or less. The measurement of the average crystal size is as described above.

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

[Example 1]
There was prepared cerium carbonate in which TREO was 50% by mass in terms of oxide, and the cerium oxide content (CeO ₂ / TREO) in TREO was 99.9% by mass in terms of oxide. 2 kg of this cerium carbonate was baked in an electric furnace at a temperature of 900 ° C. for 2 hours in an air atmosphere to obtain cerium oxide.

  When the TREO of this cerium oxide was measured, the TREO was 99% by mass. Moreover, when the crystallite diameter was calculated by X-ray diffraction measurement, the crystallite diameter was 900 mm. In this X-ray diffraction measurement, “MiniFlex” manufactured by Rigaku Corporation was used, and a Cu—Kα1 line was used using a copper target. The X-ray generation voltage was 30 kV, the X-ray generation current was 15 mA, the sampling width was 0.02 deg, and the scanning speed was 2 deg / min.

10 g of reagent-grade sodium phosphate as a dispersant is added to 500 g of cerium oxide obtained by the above baking, and is pulverized with 300 g of ion-exchanged water in a ball mill, and the average particle size (D ₅₀ ) is 0.5 μm. A slurry-like polishing liquid containing
This slurry-like polishing liquid was diluted with ion-exchanged water, and the glass substrate for hard disk was polished with a powder concentration of 10% by mass, and the polishing state was evaluated. The polishing conditions are as shown in Table 1 and below. The results are shown in Table 3 below.

(Polishing conditions)
Polishing machine: 4-way type 9B type double-side polishing machine Workpiece: Amorphous glass substrate (Vickers hardness 570Hv)
Workpiece size: 65 mmφ hard disk glass substrate (thickness: 0.635 mm) Number of processed sheets: 25 × 4 batch polishing pads: Foamed polyurethane pad (LP-77, manufactured by Rhodes)
Lower platen rotation speed: 60rpm
Polishing pressure: 120 g / cm ²
Polishing time: 30 minutes

  In addition, about 25 glass substrates for every batch, the mass before and behind grinding | polishing all 25 sheets was measured with the electronic balance, and polishing rate (micrometer / min) was calculated | required as a calculated value (average) of thickness conversion. Further, using a 200,000 lux halogen lamp as a light source, the glass surface was visually observed to determine the number of scratches (average) per polished surface. The roughness (Ra) of the surface of the glass substrate was measured in a 10 μm × 10 μm field of view with an atomic force microscope (SPA-500 manufactured by Seiko Instruments Inc.), one by one for each batch. Asked.

[Comparative Examples 1-5]
The polishing state was evaluated in the same manner as in Example 1 except that the cerium oxide-based abrasive was changed as shown in Table 1 below. The results are shown in Table 3 below.
The average particle size was adjusted by changing the classification operation conditions, and the crystallite size was adjusted by changing the firing temperature and firing conditions.

[Example 2 and Comparative Examples 6 to 10]
The polished state was evaluated in the same manner as in [Example 1 and Comparative Examples 1 to 5] except that the workpiece was changed to an amorphous glass substrate having a Vickers hardness of 600 Hv. The results are shown in Table 3 below.

[Example 3 and Comparative Examples 11-15]
The polished state was evaluated in the same manner as in [Example 1 and Comparative Examples 1 to 5] except that the workpiece was changed to a crystallized glass substrate (average crystal size: 10 μm) having a Vickers hardness of 620 Hv (see Table 2). It was. The results are shown in Table 4 below.

[Example 4 and Comparative Examples 16 to 20]
The polished state was evaluated in the same manner as in [Example 1 and Comparative Examples 1 to 5] except that the workpiece was changed to a crystallized glass substrate (average crystal size: 7 μm) having a Vickers hardness of 650 Hv (see Table 2). It was. The results are shown in Table 4 below.

  The “speed ratio”, “roughness ratio”, and “scratch ratio” in Tables 3 and 4 are the values of “polishing speed”, “surface roughness”, and “scratch” in Examples 1 to 4, respectively. The comparative example corresponding to each is evaluated relatively.

Claims (8)

A cerium oxide-based abrasive for producing a glass hard disk substrate that satisfies the following (1) to (5).
(1) The total rare earth oxide amount (TREO) is 95% by mass or more, and the cerium oxide amount with respect to the TREO is 99% by mass or more.
(2) The fluorine content is 0.05% by mass or less.
(3) The crystallite diameter of the cerium oxide calculated from powder X-ray diffraction is 700 to 1000 mm.
(4) The average particle diameter (D ₅₀ ) is 0.4 to 0.8 μm.
(5) The glass hard disk substrate has a Vickers hardness of 570 Hv or more.   The cerium oxide-based abrasive according to claim 1, wherein the glass hard disk substrate has a Vickers hardness of 600 Hv or more.   The cerium oxide-based abrasive according to claim 2, wherein the glass hard disk substrate has a Vickers hardness of 620 Hv or more.   The cerium oxide-based abrasive according to claim 3, wherein an average crystal size of crystals contained in the glass hard disk substrate is 20 nm or less.   A method for producing a glass hard disk substrate, comprising a polishing step of polishing a glass substrate having a Vickers hardness of 570 Hv or more with the polishing cloth while supplying the abrasive according to claim 1 to the polishing cloth.   The method for producing a glass hard disk substrate according to claim 5, wherein the glass substrate has a Vickers hardness of 600 Hv or more.   The method for producing a glass hard disk substrate according to claim 6, wherein the glass substrate has a Vickers hardness of 620 Hv or more.   The method for producing a glass hard disk substrate according to claim 7, wherein an average crystal size of crystals contained in the glass substrate is 20 nm or less.