Substrate for information recording media and manufacturing method thereof, information recording medium, and starting material glass plate

The present invention relates to a substrate for an information recording medium and a method for manufacturing the same, an information recording medium, and a glass base plate. The present invention relates to an information recording medium such as a magnetic disk or an optical disk, and a glass base plate used as a material for a substrate for the information recording medium.

In recent years, the progress of information technology has been remarkable, and various information recording media such as magnetic disks, magneto-optical disks, and optical disks have been actively developed for storing information.

Among this type of information recording medium, for example, a magnetic disk has a magnetic film laminated on the surface of a magnetic disk substrate formed in a donut shape, and a magnetic head slides on a data zone formed on the magnetic disk substrate. Information is recorded and played back.

As a method for manufacturing the magnetic disk substrate, a method of directly forming a magnetic material thin film without polishing a sheet-shaped glass base plate manufactured by a float method or the like has been proposed (for example, actually). Kaisho 60-159531 (publication).

However, with such a manufacturing method, it is difficult to manufacture a magnetic disk having good flatness corresponding to the recent increase in the density of data zones. Therefore, today, the glass base plate is polished to be magnetic. It is common to manufacture disk substrates.

FIG. 1 is a manufacturing process diagram showing a manufacturing method of this kind of conventional magnetic disk substrate.

That is, conventionally, after the glass base plate 101 is cut into a donut shape in the disk processing step 102, the inner and outer peripheral surfaces of the glass base plate 101 are processed to a predetermined size in the end face processing step 103, and then the surface polishing step 104. After that, the surface of the glass base plate 101 is polished, and if necessary, the substrate is strengthened in the chemical strengthening treatment step 105, and the magnetic disk substrate 107 is manufactured through the cleaning finish processing 106.

Then, in the surface polishing step 104, the surface of the glass base plate 101 is polished by being divided into three steps of a rough polishing treatment 104a, a pre-polishing treatment 104b, and a precision polishing treatment 104c.

That is, the surface of the magnetic disk substrate 107 manufactured from the sheet-shaped glass base plate 101 is microscopically formed into an uneven shape, and as shown in FIG. 2, for example, a long wavelength swell is formed according to the wavelength band. Surface swells (waviness) classified into three types of 108, medium-wavelength swells 109, and short-wavelength swells 110 are formed in a superposed manner, and the magnetic head 111 glides over the magnetic disk substrate 107 having these surface swells. Will be done.

However, with the recent increase in the density of data zones, the surface waviness characteristics have a large effect on the electromagnetic conversion characteristics, and if the followability of the magnetic head to the surface waviness is poor, malfunctions occur during recording and playback. Therefore, the magnetic disk substrate is required to have extremely high flatness.

For this reason, conventionally, the surface polishing step 104 is divided into the above-mentioned three stages, and first, rough polishing treatment 104a is performed using abrasive grains having a relatively large average particle size, thereby achieving a predetermined plate thickness dimension. The thickness of the glass base plate 101 is adjusted, and the flatness of the glass base plate 101 is corrected by reducing surface waviness, particularly long wavelength waviness having a large wavelength. After that, the pre-polishing treatment 104b and the precision polishing treatment 104c remove minute scratches formed on the surface of the glass base plate 101 and surface waviness (medium-short wavelength waviness) having a relatively small wavelength.

By the way, in recent years, the magnetic head 111 has been miniaturized in order to cope with the high density of the data zone, and the levitation height of the magnetic head 112, that is, the flying height is set low by using such a small magnetic head 111, and the magnetism is set. The development of a technique for stably sliding the head 111 on the magnetic disk substrate 107 has been actively carried out, and today, the length dimension of the magnetic head has been reduced from about 2 mm to 1 mm or less.

Since the long wavelength swell 108 has a relatively gentle swell as shown in FIG. 3, the magnetic head 111 has a constant minute gap with the magnetic disk substrate 107 along the surface of the long wavelength swell 108. It is possible to glide while maintaining t, and therefore the magnetic head 111 has become able to follow the long wavelength swell 108.

On the other hand, since the medium-wavelength swell 109 and the short-wavelength swell 110 have a steeply inclined portion 112 as shown in FIG. 4, the magnetic head 111 has a magnetic disk substrate 107 like the long-wavelength swell 108. It is not possible to glide while maintaining a constant minute interval t, and it is not possible to follow the medium wavelength swell 109 and the short wavelength swell 110. That is, if the medium-wavelength swell 109 or the short-wavelength swell 110 is present on the surface of the substrate, it causes a malfunction during the recording / playback operation. Therefore, a desired high-quality magnetic disk substrate corresponding to a high density of the data zone can be obtained. In order to obtain it, it is necessary to polish the surface so that the medium-wavelength swell 109 and the short-wavelength swell 110 are removed.

However, in the above-mentioned conventional manufacturing method, while the rough polishing treatment 104a can correct the flatness caused by the long wavelength swell, the rough polishing treatment 104a causes a new medium wavelength on the surface of the glass base plate 101. Waviness 109 and short wavelength waviness 110 are formed, so it is necessary to increase the amount of polishing in the pre-polishing step 104b and the precision polishing step 104c. Therefore, in the conventional manufacturing method, the thickness of the glass base plate 101, which is the work piece, must be formed to be thick by a predetermined value in advance, and a large amount of polishing debris removed by the polishing treatment is discharged. Therefore, there is a problem that it causes an increase in industrial waste and also causes a rise in production cost.

Moreover, since the polishing abrasive grains used in the rough polishing treatment 104a have a larger particle size than the polishing abrasive grains used in the pre-polishing treatment 104b and the precision polishing treatment 104c, the surface of the glass base plate 101 is easily scratched. In order to remove such surface scratches, the amount of polishing must be increased, and from this point as well, there is a problem that the thickness of the glass base plate 101 must be formed in advance by a predetermined value. there were.

Further, since the rough polishing process 104a is performed using abrasive grains having a large particle size after the end surface is ground and polished in the end face processing step 103, even if the end surface is mirror-finished, the grain size is coarse. It is necessary to polish again with the grains, which causes a problem that the surface roughness of the end face is lowered and the quality is deteriorated.

Furthermore, since the surface polishing step 104 is divided into three stages (coarse polishing treatment 104a, pre-polishing treatment 104b, precision polishing treatment 104c) as described above, the number of steps required for surface polishing increases and the product is completed. There is a problem that it takes a long time, and the surface of the glass base plate 101 may be scratched due to contact between substrates or contact with a jig or the like in each process, resulting in poor productivity.

The present invention has been made in view of such problems, and an object of the present invention is to provide a high-quality and highly reliable substrate for an information recording medium in which the substrate surface has extremely high-precision flatness. There is.

Another object of the present invention is to manufacture a substrate for an information recording medium, which can easily manufacture the substrate for an information recording medium in a short time and with a small amount of polishing, and can improve productivity. To provide a method.

Further, the present invention aims to provide a substrate for an information recording medium corresponding to a high recording density by using the substrate for an information recording medium, and is suitable for manufacturing a substrate for an information recording medium. It is an object of the present invention to provide a glass base plate.

Hereinafter, the outline of the present invention will be disclosed.

In today's information recording media, such as magnetic disks, the magnetic head is becoming smaller, so as described in the [Background of the Invention] section, it is possible for the magnetic head to follow long wavelength swells with large wavelengths. Therefore, it is considered that the need for a rough polishing process to generate new medium-wavelength swells and short-wavelength swells is being examined.

Regarding this point, it has already been proposed to manufacture a glass substrate for a magnetic medium (a substrate for an information recording medium) without wrapping, which is a rough polishing process (Japanese Patent Laid-Open No. 2000-351653; hereinafter, "Prior". Technology ").

By the way, in order to cope with the high density of the data zone, the surface of the glass substrate needs to have extremely high-precision flatness, and for that purpose, it is necessary to perform surface polishing treatment in some form.

However, although there is a description that the above-mentioned prior art "manufactures a substrate for an information recording medium without rough polishing (wrapping)", in a magnetic disk substrate, what kind of technical method is used to achieve high-precision flatness. No specific disclosure has been made as to whether or not it can be guaranteed.

Therefore, the present inventors used Optiflat, an optical surface swell measuring instrument manufactured by Phase Shift Technology, to measure long-wavelength swells on the surface swells formed on the glass surface.<u style="single">0.4mm ~ 5.0mm</u>The average swell Wa measured in the wavelength band of is defined as the medium swell, and the medium wavelength swell is measured by Optiflat, an optical surface swell measuring instrument manufactured by Phase Shift Technology.<u style="single">0.4mm ~ 2.0mm</u>The average swell Wa measured in the wavelength band of is defined as the short wavelength swell, which is the average measured in the wavelength band of 0.2 mm to 1.4 mm by the Zygo optical surface roughness meter Newview 200. If the surface undulation of the glass base plate is good, it is defined as roughness Ra, and if the surface waviness of the glass base plate is good, the rough polishing process is not performed by performing precision polishing using only ultrafine abrasive grains of a predetermined particle size. It was found that a substrate for an information recording medium having extremely excellent flatness can be easily obtained in a short time and with a small amount of polishing.

The present invention has been made based on such findings, and the method for manufacturing an information recording substrate according to the present invention is to obtain a substrate for an information recording medium by subjecting a glass base plate formed in a sheet shape to a surface polishing treatment. This is a method for manufacturing a substrate for an information recording medium to be manufactured. As the glass base plate, a plurality of types of surface waviness divided according to a wavelength band are formed in a superposed manner on the surface of the glass base plate, and the plurality of types of surfaces are formed. Of the swell<u style="single">Average swell measured in the wavelength range of 0.4 mm to 5.0 mm by an optical surface swell measuring device.</u>The long wavelength swell with the largest wavelength band is 6 nm or less.<u style="single">To have surface swell characteristics</u>The surface polishing treatment is characterized in that only the precision polishing treatment is performed by using the ultrafine abrasive grains having the first predetermined particle size as the free abrasive grains.

According to the above manufacturing method, since the surface polishing treatment is performed using only the ultrafine abrasive grains having the first predetermined particle size, the substrate for the information recording medium is manufactured without performing the rough polishing treatment. Therefore, medium-wavelength undulations and / or short-wavelength undulations are not newly generated by the rough polishing treatment, and a high-quality information recording medium substrate having excellent flatness can be easily produced in a short time and with a small amount of polishing. It becomes possible to manufacture. Moreover, since the amount of polishing is small, the discharge of industrial waste such as polishing debris is suppressed, and the environment is excellent.

Further, according to the further experimental results of the present inventors, before performing precision polishing, pre-polishing is performed using fine particle abrasive grains having a second predetermined particle size, which is larger than the first predetermined particle size. It has been found that the desired information recording medium substrate can be obtained in a shorter time without generating new medium-wavelength swells or short-wavelength swells by performing the treatment.

Therefore, the method for manufacturing an information recording medium substrate of the present invention is a method for producing an information recording medium substrate by subjecting a glass base plate formed in a sheet shape to a surface polishing treatment to produce an information recording medium substrate. As the glass base plate, a plurality of types of surface waviness divided according to the wavelength band are formed on the surface in a superposed manner, and among the plurality of types of surface waviness.<u style="single">Average swell measured in the wavelength range of 0.4 mm to 5.0 mm by an optical surface swell measuring device.</u>The long wavelength swell with the largest wavelength band is 6 nm or less.<u style="single">To have surface swell characteristics</u>The surface polishing treatment consists of only a pre-polishing treatment and a precision polishing treatment, and the precision polishing treatment releases ultrafine abrasive grains having a first predetermined particle size. The pre-polishing treatment is performed by using ultrafine abrasive grains having a second predetermined particle size, which is larger than the first predetermined particle size, as free abrasive grains. It is supposed to be.

Further, in order to prevent the surface of the glass base plate, which is the work piece, from being finely scratched and to avoid a decrease in the polishing rate, the first predetermined particle size has an average particle size of 0.01 μm. It is preferably ~ 1.3 μm and the 90% diameter (hereinafter referred to as 90% diameter) of the volume particle size distribution is 0.02 to 3.5 μm.

Further, when the pre-polishing treatment is performed, the average particle size of the second predetermined particle size is 0.3 μm or more from the viewpoint of avoiding the generation of minute scratches and short wavelength waviness on the substrate for the information recording medium. It is preferably 5 μm and the 90% diameter is 1 μm to 15 μm.

In the present invention, the "average particle size" means a particle size in which the volume particle size becomes 50% when the particle size is sequentially integrated from a small particle size in the volume particle size distribution, and is "90% diameter". Refers to the particle size at which the volume particle size becomes 90% when the particle size is sequentially integrated from the smaller particle size in the volume particle size distribution.

As a result of further diligent research by the present inventors, when manufacturing a sheet-shaped glass base plate, long-wavelength swell can be surely suppressed to 6 nm or less by appropriately controlling the molding conditions. Moreover, by performing the above-mentioned surface polishing treatment using the glass base plate having a long wavelength swell of 6 nm or less, a substrate for an information recording medium having extremely good surface swell characteristics and excellent flatness can be easily obtained. I got the finding that I can do it.

Therefore, in the method for manufacturing a substrate for an information recording medium according to the present invention, a plurality of types of surface waviness classified according to a wavelength band are formed in a superposed manner on the surface of a glass base plate, and the surface waviness is said to be It is characterized by using a glass base plate formed with a long wavelength swell having the largest wavelength band of 6 nm or less.

Further, the long wavelength swell of the glass base plate is preferably formed to 0.4 nm or more in consideration of productivity, and in order to efficiently perform precision polishing, the short wavelength swell having the smallest wavelength band is 0.1. It is preferable to form the glass base plate at nm to 0.7 nm so that the medium wavelength swell belonging to the middle between the long wavelength swell and the short wavelength swell is 0.25 nm to 2 nm.

Further, as a method for producing a glass base plate in which long-wavelength swell is suppressed to 6 nm or less, it is preferable to manufacture the glass base plate by a float method in consideration of productivity and the like. It is preferably produced from ribbon-shaped glass in a predetermined high temperature state formed by pouring.

Further, in order to reduce the polishing time as much as possible while removing minute scratches on the surface of the glass base plate by the polishing treatment, the amount of polishing polished by the surface polishing treatment is 1 μm from the surface of the glass base plate. It is preferably ~ 75 μm, preferably 1 μm to 25 μm.

Further, in order to maintain the polishing rate and perform precision polishing without damaging the glass base plate, the ultrafine abrasive grains used in the surface polishing treatment are cerium oxide, aluminum oxide, and zirconium oxide. , Silicon oxide, and manganese oxide, and at least one selected substance, particularly cerium oxide, is preferably used.

Further, the substrate for an information recording medium according to the present invention is a substrate for an information recording medium in which a plurality of types of surface waviness classified according to a wavelength band are formed so as to be superimposed on the surface of the glass base plate. It is characterized by being manufactured by any of the manufacturing methods, and the long wavelength swell having the largest wavelength band is formed at 0.3 nm to 1.2 nm, and the short wavelength swell having the smallest wavelength band is 0.1 nm. It is characterized in that it is formed at ~ 0.6 nm, and a medium wavelength swell that belongs to the middle between the long wavelength swell and the short wavelength swell is formed at 0.2 nm to 0.9 nm.

According to the above configuration, a substrate for an information recording medium having good surface waviness characteristics and extremely excellent flatness can be easily obtained in a short time.

Further, the information recording medium according to the present invention is characterized in that an information recording layer is laminated on the surface of the information recording medium substrate.

According to the above configuration, it is possible to easily obtain an information recording medium corresponding to a high density of data zones having extremely excellent flatness.

Further, the glass base plate according to the present invention is a glass base plate in which a plurality of types of surface waviness classified according to a wavelength band are formed so as to overlap the surface of the glass base plate, and is the most in the wavelength band. It is characterized by a large long-wavelength swell being formed at 6 nm or less, a short-wavelength swell having the smallest wavelength band of 0.7 nm or less, and an intermediate between the long-wavelength swell and the short-wavelength swell. It is characterized in that the medium wavelength swell to which it belongs is formed to be 2 nm or less, and is also characterized in that it is produced from ribbon-shaped glass in a predetermined high temperature state formed by pouring a glass raw material onto molten tin.

According to the above-mentioned glass base plate, a glass base plate in which long-wavelength waviness is suppressed by the float method can be easily obtained, and a glass material suitable for manufacturing a substrate for an information recording medium can be provided.

FIG. 1 is a manufacturing process diagram showing a conventional manufacturing method for a substrate for an information recording medium. Fig. 2 is a diagram schematically showing the state of surface waviness of a conventional glass base plate. Fig. 3 is a schematic diagram for explaining the relationship between the magnetic head and the magnetic disk substrate in the case of long wavelength swell. FIG. 4 is a schematic diagram for explaining the relationship between the magnetic head and the magnetic disk substrate in the case of medium-wavelength swell or short-wavelength swell. FIG. 5 is a cross-sectional view of a main part schematically showing an embodiment of an information recording medium according to the present invention. FIG. 6 is a manufacturing process diagram showing an embodiment of a method for manufacturing a substrate for an information recording medium according to the present invention. FIG. 7 is a schematic structural diagram showing an embodiment of a float plate glass manufacturing apparatus. FIG. 8 is a manufacturing process diagram showing an embodiment of a method for manufacturing a substrate for an information recording medium according to the present invention, and FIG. FIG. 9 is a schematic structural diagram showing an embodiment of a down draw plate glass manufacturing apparatus.

Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

FIG. 5 is a cross-sectional view schematically showing an embodiment of a magnetic disk as an information recording medium according to the present invention, wherein the magnetic disk has a base layer 2, a magnetic layer 3, and a protective layer 4. They are sequentially laminated on the surface of the magnetic disk substrate 1 by a well-known sputtering method.

The magnetic disk substrate 1 is manufactured by a manufacturing method described later, and fine uneven surface waviness is formed on the surface of the substrate. Specifically, the surface waviness is classified into three types (long wavelength waviness, medium wavelength waviness, and short wavelength) defined in the section of [Disclosure of the Invention], and the magnetic disk substrate 1 has a long wavelength waviness. It is formed so that the medium wavelength swell is 0.3 nm to 1.2 nm, the medium wavelength swell is 0.2 nm to 0.9 nm, and the short wavelength swell is 0.1 nm to 0.6 nm.

Next, the reason why the surface waviness of the magnetic disk substrate 1 is set within the above range will be described.

When the long-wavelength swell exceeds 1.2 nm, the medium-wavelength swell exceeds 0.9 nm, and the short-wavelength swell exceeds 0.6 nm, the surface swell becomes large and glides on today's high-density magnetic disk substrate 1 at a low flying height. The tracking of the magnetic head is hindered, and a high-quality magnetic disk substrate 1 cannot be obtained. On the other hand, even if the long wavelength swell is less than 0.3 nm, the medium wavelength swell is less than 0.2 nm, and the short wavelength swell is less than 0.1 nm, the quality becomes saturated and further quality improvement cannot be expected. Therefore, in the present embodiment, the magnetic disk substrate 1 is manufactured so that the long wavelength swell is 0.3 nm to 1.2 nm, the medium wavelength swell is 0.2 nm to 0.9 nm, and the short wavelength swell is 0.1 nm to 0.6 nm. did.

Since the surface of the magnetic disk substrate 1 is formed in a superposed manner with three types of surface waviness classified according to the wavelength band, even one type of surface waviness out of the three types of surface waviness is out of the above range. In this case, the electromagnetic conversion characteristics of the magnetic head deteriorate and the quality of the magnetic disk substrate 1 deteriorates. Therefore, the magnetic disk substrate 1 needs to satisfy all the ranges of the above-mentioned three types of surface waviness.

Further, in this magnetic disk, CrMo, Cr, CrV, etc. can be used as the base layer 2, and the magnetic layer 3 can secure excellent information recording / reproduction characteristics and film adhesion. , CoPtCr, CoPtCrTa and other cobalt-based alloys can be used. A carbon-based material such as hydrogenated carbon can be used as the protective layer 4.

Next, the manufacturing method of the magnetic disk substrate 1 will be described in detail.

FIG. 6 is a manufacturing process diagram showing one embodiment (first embodiment) of the method for manufacturing the magnetic disk substrate 1, wherein the magnetic disk substrate 1 is, for example, a float plate glass manufactured by a float method. Is a glass base plate 5, and is manufactured through a disk processing process 6 end face processing process 7 surface polishing process 8 chemical strengthening process 9 finish cleaning process 10.

FIG. 7 is a schematic configuration diagram schematically showing a float plate glass manufacturing apparatus, in which a predetermined glass material powder is charged and the glass material powder is melted in a predetermined high temperature atmosphere. The main parts are a molten kiln 11, a sealed molding tank 13 in which molten tin 12 is contained and a reducing atmosphere, and a slow cooling kiln 15 that slowly cools the glass ribbon 14 drawn out from the molding tank 13. It is configured as.

The glass material is not particularly limited, and SiO is used.₂, Na₂Soda lime glass with O and CaO as the main components, SiO₂, Al₂O₃, Na₂O, Li₂Aluminosilicate glass containing O as the main component, or borosilicate glass, Li₂O-SiO₂System glass, Li₂O-Al₂O₃-SiO₂System glass, RO-Al₂O₃-SiO₂Based glass (however, R = Mg, Ca, Sr, or Ba) can be used, and ZrO is used for these glass materials.₂And TiO₂It is possible to use glass for tempering glass to which the above is added, or crystallized glass that is not chemically strengthened.

Then, in the float plate glass manufacturing apparatus, when the glass material powder prepared to a predetermined composition ratio is put into the melting kiln 11 heated to 1500 to 1600 ° C, the glass material powder is melted inside the melting kiln 11. The molten glass is formed, and the molten glass flows into the molding tank 13. The forming tank 13 contains the molten tin 12 as described above, but since the molten glass has a lighter specific gravity than the molten tin 12, it moves in the direction of arrow A while floating on the molten tin 12. I will do it. That is, as a result of the molten glass floating on the molten tin 12, it becomes a glass ribbon 14 having a predetermined plate thickness, which is formed into a ribbon shape.

The glass ribbon 14 produced in this manner is pulled up to the slow cooling kiln 15 via the roller conveyor 16 and conveyed in the direction of arrow B. Then, the slow cooling kiln 15 is cooled to room temperature while preventing the occurrence of strain, and then the glass ribbon 14 cooled to room temperature is discharged from the slow cooling kiln 15 and cut into a square shape to form one manufacturing rod. A large number of glass base plates 5 are manufactured from.

By the way, in the float plate glass manufacturing apparatus, the lower surface of the glass ribbon 14 in contact with the molten tin 12 is cooled while being in contact with the molten tin 12 having a free surface, so that the molten tin 12 is macroscopically extremely flat. The upper surface of the glass ribbon 14 in contact with the space 17 above the glass ribbon 14 is formed into a sheet having a predetermined thickness while spreading in the horizontal direction due to viscous flow. Therefore, it is considered that the glass ribbon 14 is macroscopically excellent in flatness on both the upper and lower sides.

However, the molten tin 12 has a temperature gradient in the direction of arrow A, and the temperature is not uniform and has a constant temperature distribution even in the width direction of the glass ribbon 14 (in FIG. 7, the direction perpendicular to the paper surface). Furthermore, the temperature is not uniform even in the space portion 17. Therefore, although the surface (upper and lower surfaces) of the glass ribbon 14 is macroscopically excellent in flatness, it is usually formed with a considerably large uneven surface waviness microscopically. Even if the precision polishing treatment described later is performed with such a large uneven surface waviness, the surface waviness cannot be reduced to a desired value in a short time and with a small amount of polishing. Moreover, in order to remove such a large surface waviness, it is necessary to form a thick glass base plate 5 in advance.

Therefore, in the present embodiment, the glass base plate is formed so that the surface waviness of the glass base plate 5, particularly the long wavelength waviness, is reduced by appropriately controlling the temperature in the molding tank 13 and controlling the molding conditions. doing.

Specifically, for example, the temperature gradient of the molten tin 12 in contact with the glass ribbon 14 in the arrow A direction is appropriately controlled, and the temperature is controlled so that the temperature distribution in the width direction of the glass ribbon 14 becomes as small as possible. In addition, by controlling the convection generated in the molten tin 12, and further controlling the molding conditions so that the temperature distribution of the space 17 above the molten tin 12 and the turbulence of the convection are reduced, the desired surface waviness characteristics can be obtained. The glass base plate 5 having the glass base plate 5 can be manufactured. In particular, since the glass ribbon 14 becomes more viscous as it moves in the direction of arrow A, the temperature distribution in the width direction of the glass ribbon 14 near the outlet of the molding tank 13 is made as uniform as possible, and the outside to the molten tin 12 is made uniform. It is preferable to block the slight vibration from the surface in order to obtain the above-mentioned surface waviness characteristic.

Specifically, the surface swell of the glass base plate 5 is such that the long wavelength swell is 0.4 nm to 6 nm, the medium wavelength swell is 0.25 nm to 2 nm, and the short wavelength swell is 0.1 nm to 0.7 nm. It is preferable to form the plate 5.

That is, when the long wavelength swell exceeds 6 nm, the medium wavelength swell exceeds 2 nm, and the short wavelength swell exceeds 0.7 nm, respectively, in order to obtain the magnetic disk substrate 1 having the desired good flatness, the surface polishing treatment described later is performed. When performing precision polishing, the amount of polishing must be increased, and the polishing time also becomes long. On the other hand, it is technically difficult to control various molding conditions so that the long wavelength swell is less than 0.4 nm, the medium wavelength swell is less than 0.25 nm, and the short wavelength swell is less than 0.1 nm. Invite soaring prices.

Therefore, in the present embodiment, the molding conditions are controlled so that the long wavelength swell is 0.4 nm to 6 nm, the medium wavelength swell is 0.25 nm to 2 nm, and the short wavelength swell is 0.1 nm to 0.7 nm. Was decided to be manufactured.

After that, the glass base plate 5 having the surface waviness characteristic is subjected to various processing treatments, and the magnetic disk substrate 1 as a product is manufactured through the above-mentioned steps.

Hereinafter, each of the above steps will be described in sequence.

(1) Disk processing process 6 In the disk processing step 6, a cutter equipped with cemented carbide or diamond is used to simultaneously cut along the outer peripheral surface and the inner peripheral surface so as to have a predetermined outer diameter and a predetermined inner diameter, whereby the concentricity is excellent. Manufacture a donut-shaped glass base plate 5.

In the present embodiment, the outer peripheral surface and the inner peripheral surface are cut at the same time, but first the outer peripheral surface is cut so as to have a predetermined outer diameter, and then a predetermined inner diameter is obtained using a cylindrical diamond grindstone. It may be drilled so as to have it, or it may be manufactured by a pressing method so that the outer diameter has a predetermined size, and then drilled with a diamond grindstone so as to have a predetermined inner diameter.

(2) End face processing process 7 In the end face processing step 7, the end face is ground and polished so that the outer diameter dimension and the inner diameter dimension of the donut-shaped glass base plate 5 become the outer diameter dimension and the inner diameter dimension of the magnetic disk substrate 1 which is a product, and the glass substrate is processed. To manufacture. Specifically, using a grindstone to which diamond abrasive grains are attached, grinding of the inner and outer peripheral surfaces and chamfering of the corners of the inner and outer peripheral surfaces are performed in two stages using diamond abrasive grains with different grain sizes. , Manufacture glass substrates.

As for the grain size of the diamond abrasive grains, diamond abrasive grains having an optimum grain size are appropriately used according to the required quality. Further, in the disk processing step 6 described above, if the disk has already been processed to a size close to the outer diameter dimension and the inner diameter dimension of the magnetic disk substrate 1 which is a product, it is not necessary to perform the grinding process in two steps. Needless to say, the grinding process can be done in one step.

And after this, CeO as a free abrasive grain₂Using (cerium oxide) abrasive grains, the end face (including the chamfered portion; hereinafter the same) is polished so that the surface roughness Ra of the end face is equal to or less than a predetermined value, and the end face is smoothed.

(2) Surface polishing process 8 In the surface polishing step 8, free abrasive grains (ultrafine abrasive grains) having an average particle size of 0.01 μm to 1.3 μm and a 90% diameter of 0.02 μm to 3.5 μm are used to obtain free abrasive grains having such a particle size. The surface of the glass substrate was subjected to precision polishing treatment 8a while supplying the polishing agent dispersed in the polishing liquid to the surface of the glass substrate.

The reason why the particle size of the free abrasive grains is limited in this way is as follows.

That is, when the average particle size exceeds 1.3 μm and / or the 90% diameter exceeds 3.5 μm, the particle size of the free abrasive grains becomes large as a whole. And short wavelength waviness may be generated, and the surface of the glass substrate is easily scratched by the free abrasive grains. On the other hand, when the average particle size is less than 0.01 μm and / or the 90% diameter is less than 0.02 μm, the particle size of the free abrasive grains becomes small, so that the time required for the polishing process becomes long and the productivity decreases.

Therefore, in the present embodiment, the precision polishing treatment 8a is performed using free abrasive grains having an average particle size of 0.01 μm to 1.3 μm and a 90% diameter of 0.02 μm to 3.5 μm.

Further, in the precision polishing treatment 8a, the polishing amount was set to 1 μm to 75 μm, preferably 1 μm to 25 μm from the surface of the glass substrate. That is, when precision polishing is performed on a glass substrate having the above-mentioned good surface waviness using the free abrasive grains having the above-mentioned particle size, if the polishing amount is less than 1 μm, the polishing amount is small and therefore the surface of the glass substrate If the formed minute scratches cannot be sufficiently removed, while the polishing amount exceeds 75 μm (preferably 25 μm), excessive polishing will be performed, and polishing time will be wasted. It causes a decrease in productivity.

Therefore, in the present embodiment, the polishing amount in the precision polishing treatment 8a is set to 1 μm to 75 μm, preferably 1 μm to 25 μm from the surface of the glass substrate.

The type of free abrasive grains is not particularly limited, and CeO₂And La₂O₃Rare earth oxides such as ZrO₂, MnO₂, Al₂O₃, SiO₂(Coroidal silica) etc. can be used, but from the viewpoint of obtaining excellent polishing efficiency, rare earth oxides, especially CeO₂It is preferable to use system abrasive grains.

Further, the polishing pad used for polishing is not particularly limited, and a non-woven fabric or a foam can be used, but it is formed from a layer (NAP layer) in which an opening is formed by finishing the surface of a continuous foam layer and a base layer. The use of suede pads is preferable from the viewpoint of preventing the formation of scratches on the glass substrate.

In the present embodiment, the polishing rate in the precision polishing process 8a is in the range of 0.1 μm / min to 0.8 μm / min.

Further, the glass substrate subjected to the precision polishing treatment 8a is washed with an acidic aqueous solution, an alkaline aqueous solution, pure water, or the like. (3) Chemical strengthening process 9 In the chemical strengthening treatment step 9, a molten salt adjusted to a predetermined temperature, for example, potassium nitrate (KNO)₃) And sodium nitrate (NaNO)₃) Is immersed in a molten salt consisting of a mixed solution for a predetermined time, and Li in the chemical composition of the glass substrate⁺¹And Na⁺¹The K with a large ionic radius⁺¹A chemical strengthening process is performed to exchange ions with the ions. Then, by performing such a chemical strengthening treatment, the surface compressive stress is increased, and it is possible to prevent the magnetic disk from being damaged even if it is rotated at high speed.

After that, the glass substrate is slowly cooled to around room temperature, and the molten salt adhering to the glass substrate is washed off in warm pure water.

The chemical strengthening treatment step 9 may be omitted depending on the required strength of the magnetic disk substrate 1, and if the glass base plate 5 is made of crystallized glass, it is chemically strengthened. Is not possible, so it is usually omitted.

(4) Finish cleaning process 10 In the finish cleaning step 10, the glass substrate which has been subjected to precision polishing and, if necessary, chemically strengthened is immersed in an acidic aqueous solution, an alkaline aqueous solution, or a mixed solution in which pure water is appropriately combined, and if necessary. The magnetic disk substrate 1 as a product is manufactured by cleaning while irradiating with ultrasonic waves to remove impurities such as abrasives adhering to the surface of the glass substrate and molten salts adhering during chemical treatment.

Then, as described above, in the present embodiment, the surface polishing treatment is performed by free abrasive grains (super) having an average particle size of 0.01 μm to 1.3 μm and a 90% diameter of 0.02 to 3.5 μm (first predetermined particle size). Since the precision polishing process 8a is performed using only fine abrasive grains), the substrate for the information recording medium can be manufactured without performing the rough polishing process. Therefore, the rough polishing process causes medium wavelength undulations and / or short lengths. No new wavelength swell is generated, and by selecting a glass base plate with good surface swell characteristics, a high-quality information recording medium substrate with excellent flatness can be polished in a short time and with a small amount of polishing. Can be easily manufactured with. Moreover, since the amount of polishing is small, the discharge of industrial waste such as polishing debris is suppressed, and the environment is excellent.

FIG. 8 is a manufacturing process diagram showing a second embodiment of the magnetic disk substrate as the information recording medium according to the present invention. In the present embodiment, the precision polishing process 8a'is performed in the surface polishing step 8'. The pre-polishing process 8b'is performed before the process, thereby further shortening the time required for the surface polishing step 8'.

That is, in the pre-polishing treatment 8b', the free abrasive grains (fine particle abrasive grains) having a larger particle size than the free abrasive grains used in the precision polishing treatment 8a', specifically, the average particle size is 0.3 μm to 5 μm and 90. Pre-polishing is performed using free abrasive grains with a% diameter of 1 μm to 15 μm.

The reason why the free abrasive grains having the above particle size are used in the pre-polishing treatment 8b'is as follows.

That is, if the average particle size exceeds 5 μm and / or the 90% diameter exceeds 15 μm, the particle size may increase, leading to the occurrence of minute scratches or the growth of short wavelength swells. On the other hand, if the average particle size is less than 0.3 μm and / or the 90% diameter is less than 1 μm, the intended purpose of shortening the polishing time cannot be achieved because the particle size is small. Therefore, in the present embodiment, the pre-polishing treatment 8b'was performed using free abrasive grains having an average particle size of 0.3 μm to 5 μm and a 90% diameter of 1 μm to 15 μm.

Further, as the free abrasive grains used in the pre-polishing treatment 8b'and the precision polishing treatment 8a', the same free abrasive grains as those in the precision polishing treatment 8a in the first embodiment can be used, and pre-polishing can be used. It is also preferable to use different free abrasive grains for the treatment 8b'and the precision polishing treatment 8a'. For example, for each of the pre-polishing treatment 8b'and the precision polishing treatment 8a', Al₂O₃And CeO₂, CeO₂And SiO₂(Coroidal Silica), ZrO₂And CeO₂, CeO₂And MnO₂Polishing treatment may be performed in combination with each other.

As described above, in the second embodiment, the average particle size larger than the particle size of the free abrasive grains used in the precision polishing 8a'is 0.3 μm to 5 μm, and the 90% diameter is 1 μm to 15 μm (the second embodiment). Pre-polishing treatment 8b'is performed using free abrasive grains (ultrafine abrasive grains) having a predetermined particle size of 2), and then precision polishing treatment 8a' is performed, so that the polishing time required for surface polishing is further shortened. It is possible to improve the productivity of the magnetic disk substrate 1 having high quality and excellent reliability.

FIG. 9 is a schematic configuration diagram schematically showing a down-draw plate glass manufacturing apparatus as another embodiment of the glass base plate manufacturing apparatus, and the down-draw plate glass manufacturing apparatus is charged with a predetermined glass material powder. A melting kiln 21 for melting the glass material powder in a predetermined high temperature atmosphere, a working tank 22 for adjusting the molten glass (molten glass) to a predetermined temperature, and a platinum orifice are formed in the working tank. A slot 23 for pulling out molten glass from 22 and a slow cooling kiln 24 for slowly cooling the ribbon-shaped glass ribbon 25 pulled out from the slot 23 are mainly configured.

Then, in the down draw plate glass manufacturing apparatus configured in this way, when the glass material powder adjusted to a predetermined composition ratio is heated to 1500 ° C to 1600 ° C and put into the melting kiln 21, the glass material powder is charged. Is melted inside the melting kiln 21 to become molten glass, and the molten glass flows into the working tank 22 to be homogenized in the working tank 22 and adjusted to a temperature suitable for molding. Then, the molten glass flows downward from the work tank 22 through the slot 23, and is adjusted to a predetermined speed by gravity (indicated by the arrow C) and the rotational force of the roller 26, and a glass ribbon 25 having a predetermined thickness is manufactured. , The glass ribbon 25 is cut into a predetermined square shape to obtain a glass base plate.

In the down draw method, the surface quality such as the thickness distribution and flatness (waviness characteristic) of the glass ribbon 25 (glass base plate) is determined by the temperature of the molten glass entering the slot 23 and the slot 23 itself. It is also the temperature distribution in the width direction of the slot 23. For this reason, slot 23 uses a platinum orifice as shown in FIG. 9 and a fusion pipe made of refractory so that a high quality glass ribbon 25 can be obtained. It has been devised.

Then, in this down draw method, the glass ribbon 25 pulled out from the slot 23 descends by gravity in the free space in the slow cooling kiln 24 while its end being sandwiched by the roller 26, but the glass ribbon 25 (glass) The descending speed and temperature gradient of the molten glass, or the temperature distribution in the width direction and the flow of the airflow in the free space through which it passes are controlled so that the surface undulation of the base plate) becomes smaller, so that the long wavelength undulation is 0.4 nm ~ We manufacture glass ribbon 25 (glass base plate) with surface waviness of 6 nm, medium wavelength waviness of 0.25 nm to 2 nm, and short wavelength waviness of 0.1 nm to 0.7 nm.

The present invention is not limited to the above embodiment. In the above embodiment, the glass base plate 5 is manufactured by the float method or the down draw method, but the long wavelength swell is 0.4 nm to 6 nm, medium. The production method is not particularly limited as long as it is possible to produce the glass base plate 5 having a surface undulation having a wavelength undulation of 0.25 nm to 2 nm and a short wavelength undulation of 0.1 nm to 0.7 nm. For example, a glass base material formed into a sheet through a melting tank or the like is reheated in a heating furnace to reduce the glass viscosity while pulling it downward or laterally to reduce the plate thickness, and then in a slow-cooling kiln. It may be manufactured by using the redraw method of slow cooling.

[Example] Next, an embodiment of the present invention will be specifically described.

(First Example) The present inventors have performed test pieces (Examples 1 to 5) that have been subjected to precision polishing only using float plate glass (glass base plate) having good surface waviness characteristics, before performing precision polishing treatment. Specimens that have been polished (Examples 6 to 8), Specimens that have been subjected to precision polishing only using down-draw plate glass (glass base plate) with good surface waviness characteristics (Example 9), Test pieces in which rough polishing treatment is incorporated into the surface polishing process (Comparative Example 1, Comparative Example 2), and test pieces in which various surface polishing is performed using a glass base plate whose surface waviness is outside the range of the present invention (Comparative Example 3). ~ Comparative Example 5) was prepared, and the surface waviness of each test piece was measured before and after the surface polishing treatment, that is, immediately after the end face polishing was completed and after the precision polishing treatment was completed, and the surface texture was evaluated.

Table 1 shows the manufacturing method, surface texture, and surface polishing treatment of the glass base plate, and Table 2 shows the surface texture of the magnetic disk substrate obtained after the surface polishing treatment.

Long-wavelength swells and medium-wavelength swells are measured in the range of 38 mm to 84 mm in diameter with Optiflat, an optical surface swell measuring instrument manufactured by Phase Shift Technology, and short-wavelength swells are measured by Zygo (Zygo). Zygo)'s optical surface unevenness meter Newview 200 was used to measure at three points: the inner circumference, the outer circumference, and the intermediate circumference between the inner circumference and the outer circumference, and the average value was calculated. In addition, the measured values in the table show the average value of the number of test pieces (300 or 500) of each Example or Comparative Example.

The amount of polishing was calculated by measuring the thickness before and after polishing using a micrometer manufactured by Mitutoyo.

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<tables num="2"><img file="JP4947754B2_D0002.tif" /></tables>

Hereinafter, the procedure for preparing the test pieces of each Example and Comparative Example will be described.

(Example 1) First, the present inventors manufactured a lithium-alumina-silica-based glass base plate using a float plate glass manufacturing apparatus (see FIG. 7). Specifically, SiO₂: 70mol%, Al₂O₃: 15mol%, Li₂O: 7mol%, Na₂Each glass material powder is put into a melting kiln so that O: 8 mol% is melted inside the melting kiln and poured into a molding tank, whereby a glass ribbon is produced, and then good surface waviness characteristics are obtained. As described above, the glass ribbon is moved on the molten tin while controlling the temperature of the molding tank under predetermined molding conditions, carried out from the molding tank to a slow cooling kiln, and the ribbon glass obtained from such a production lot is cut into a square shape. , 300 glass base plates with a thickness of about 1 mm were obtained.

Next, using a cutter with diamonds, the glass base plate is cut simultaneously along the outer and inner peripheral surfaces so that the outer diameter is 95 mm and the inner diameter is 25 mm, and the glass base plate is cut into a donut shape. processed.

Next, the inner and outer peripheral surfaces are ground and the corners are chamfered using a grindstone to which diamond abrasive grains are attached, and then CeO.₂The end face including the chamfered portion was polished using abrasive grains, and the outer peripheral surface and the inner peripheral surface were mirror-finished.

Next, CeO with an average particle size of 1 μm and a 90% diameter of 3 μm₂Using abrasive grains, CeO₂The test piece of Example 1 was prepared by performing a precision polishing treatment for 40 minutes while supplying an abrasive in which abrasive grains were dispersed in a polishing liquid to the surface of a glass base plate. A suede pad was used as the polishing pad.

(Example 2) After obtaining 300 glass base plates from the same production lot as in Example 1 and performing the same disk processing and end face processing as in Example 1, CeO as in Example 1.₂Precision polishing treatment was performed for 60 minutes using abrasive grains to prepare a test piece of Example 2.

(Example 3) Using glass powder having the same composition as in Example 1, ribbon glass is manufactured in another production lot with substantially the same molding conditions, and the ribbon glass is cut into a square shape to form a glass base plate having a plate thickness of about 1 mm. I got 500 pieces.

Next, after performing the same disk processing and end face processing as in Example 1, CeO having an average particle size of 1 μm and a 90% diameter of 2.8 μm.₂Precision polishing treatment was performed for 60 minutes using abrasive grains to prepare a test piece of Example 3.

(Example 4) After obtaining 300 glass base plates from the same production lot as in Example 3 and performing the same disk processing and end face processing as in Example 1, CeO having an average particle size of 0.3 μm and a 90% diameter of 1.2 μm.₂Precision polishing treatment was performed for 120 minutes using abrasive grains to prepare a test piece of Example 4.

(Example 5) Using glass powder having the same composition as in Example 1, a glass ribbon is manufactured by changing the molding conditions so that the surface waviness becomes smaller, and the glass ribbon is cut into a square shape to form a glass element having a plate thickness of about 1 mm. Obtained 300 boards.

Next, after performing the same disk processing and end face processing as in Example 1, the CeO as in Example 1₂A test piece of Example 5 was prepared by performing a precision polishing treatment for 20 minutes using abrasive grains.

(Example 6) After obtaining 300 glass base plates from the same production lot as in Example 1 and performing the same disk processing and end face processing as in Example 1, CeO with an average particle size of 3 μm and a 90% diameter of 8 μm.₂Pre-polishing with abrasive grains for 7 minutes, followed by CeO with an average particle size of 1 μm and a 90% diameter of 3 μm, as in Example 1.₂Precision polishing treatment was performed for 20 minutes using abrasive grains to prepare a test piece of Example 6. That is, in Example 6, a 7-minute pre-polishing treatment and a 20-minute precision polishing treatment were performed, and therefore a total of 27 minutes of surface polishing was performed.

(Example 7) After obtaining 500 glass base plates from the same production lot as in Example 3 and performing disk processing and end face processing in the same manner as in Example 1, CeO with an average particle size of 3 μm and a 90% diameter of 7.5 μm.₂Pre-polishing with abrasive grains for 9 minutes, followed by CeO with an average particle size of 0.3 μm and a 90% diameter of 1.2 μm, as in Example 4.₂Precision polishing treatment was performed for 30 minutes using abrasive grains to prepare a test piece of Example 7. That is, in Example 7, 9 minutes of pre-polishing treatment and 30 minutes of precision polishing treatment were performed, and therefore a total of 39 minutes of surface polishing was performed.

(Example 8) After obtaining 500 glass base plates from the same production lot as in Example 3 and performing disk processing and end face processing in the same manner as in Example 1, CeO with an average particle size of 1 μm and a 90% diameter of 3 μm.₂Pre-polishing was performed for 40 minutes using abrasive grains, and then precision polishing was performed for 30 minutes using colloidal silica abrasive grains with an average particle size of 0.02 μm and a 90% diameter of 0.03 μm. A test piece was prepared. That is, in Example 8, 40 minutes of pre-polishing treatment and 30 minutes of precision polishing treatment were performed, and therefore a total of 70 minutes of surface polishing was performed.

(Example 9) A glass base plate was produced by a down-draw method using a glass material powder having the same composition as that of Example 1. That is, the glass material powder was put into a molten kiln to prepare molten glass, and the molten glass was allowed to flow downward from a platinum orifice (slot) to form a sheet having a plate thickness of about 1 mm by using gravity. After that, it was slowly cooled in a slow-cooling kiln and cut into squares to obtain 300 glass base plates.

Next, in the same manner as in Example 1, disk processing, end face processing, and precision polishing treatment were performed to prepare a test piece of Example 9.

(Comparative example 1) 300 glass base plates were obtained from the same production lot as in Example 1, and after performing the same disk processing and end face processing as in Example 1, rough polishing was performed. That is, Al with an average particle size of 5.5 μm and a 90% diameter of 10 μm.₂O₃Rough polishing was performed for 35 minutes using abrasive grains. Then, after that, precision polishing treatment was performed in the same manner as in Example 1 to prepare a test piece of Comparative Example 1. That is, in Comparative Example 1, a rough polishing treatment for 35 minutes and a precision polishing treatment for 40 minutes were performed, and therefore a total of 75 minutes of surface polishing was performed.

(Comparative example 2) After obtaining 300 glass base plates from the same production lot as in Example 1 and performing the same disk processing and end face processing as in Example 1, rough polishing treatment, pre-polishing treatment, and precision polishing are performed as in the conventional case. The surface was polished in three steps. That is, first, Al with an average particle size of 9 μm and a 90% diameter of 20 μm.₂O₃Rough polishing with abrasive grains for 20 minutes, then CeO with an average particle size of 3 μm and a 90% diameter of 7.5 μm₂Rough polishing treatment is performed for 30 minutes using abrasive grains, and then, as in Example 1, CeO having an average particle size of 1 μm and a 90% diameter of 3 μm.₂Precision polishing treatment was performed for 40 minutes using abrasive grains to prepare a test piece of Comparative Example 2. That is, in Comparative Example 2, a rough polishing treatment for 20 minutes, a pre-polishing treatment for 30 minutes, and a precision polishing treatment for 40 minutes were performed, and therefore a total of 90 minutes of surface polishing was performed.

(Comparative example 3) A glass ribbon having the same composition as that of Example 1 is used to manufacture a glass ribbon without sufficiently controlling the temperature of the molding tank, and the glass ribbon is cut into a square shape to obtain a glass base plate having a plate thickness of about 1 mm. I got 300 pieces.

Next, after performing the same disk processing and end face processing as in Example 1, rough polishing treatment was performed for 20 minutes in the same manner as in Comparative Example 2, and then precision polishing treatment was performed for 35 minutes in the same manner as in Example 1. A test piece of Comparative Example 3 was prepared. That is, in Comparative Example 3, a rough polishing treatment for 20 minutes and a precision polishing treatment for 35 minutes were performed, and therefore a total of 55 minutes of surface polishing was performed.

(Comparative example 4) 300 glass base plates were obtained from the same production lot as in Comparative Example 3, then disk processing and end face processing were performed in the same manner as in Example 1, and then pre-polishing for 60 minutes under the same conditions as in Example 6. The test piece of Comparative Example 4 was prepared by performing the treatment and the precision polishing treatment for 40 minutes.

(Comparative example 5) After obtaining 300 glass base plates from the same production lot as in Comparative Example 3 and performing disk processing and end face processing in the same manner as in Example 1, CeO in the same manner as in Example 1.₂A test piece of Comparative Example 5 was prepared by precision polishing for 200 minutes using abrasive grains.

As is clear from the measurement results in Tables 1 and 2, the glass base plate of Example 1 has a small long-wavelength swell of 3.5 nm, and medium-wavelength swell and short-wavelength swell of 1.6 nm and 0.7 nm, respectively. Due to its small size, even on a magnetic disk substrate after precision polishing, long-wavelength swells are as small as 1.0 nm, medium-wavelength swells are as small as 0.6 nm, and short-wavelength swells are as small as 0.4 nm. We were able to manufacture a magnetic disk substrate with excellent properties. Moreover, the amount of polishing was as small as 10 μm, and therefore excellent surface waviness characteristics could be obtained with a small amount of polishing. In addition, when the presence or absence of micro-scratches was visually confirmed, a good result was obtained with 1 out of 300, and it was found that the probability of micro-scratches was extremely low.

Example 2 is a test piece in which the polishing time is 1.5 times longer than that in Example 1. Since the polishing time is lengthened, the polishing amount is slightly increased to 15 μm, but the surface waviness characteristics are improved.

In Example 3, a magnetic disk substrate was produced from a glass base plate under substantially the same conditions as in Example 2, and it can be seen that surface waviness characteristics substantially equivalent to those in Example 2 were obtained.

Example 4 is CeO as a free abrasive grain.₂Compared to Examples 1 to 3, the grain size of the abrasive grains is as small as 0.3 μm for the average abrasive grains and 1.2 μm for the 90% diameter, so the polishing speed is slightly slower, and therefore polishing takes 120 minutes. The amount is as small as 12 μm, but the short wavelength swell is improved. That is, it was found that short-wavelength waviness can be reduced by performing precision polishing using fine free abrasive grains.

In Example 5, the surface waviness characteristics of the glass base plate, particularly the long wavelength waviness, are remarkably superior to those of Examples 1 to 4, so that the polishing time is as short as 20 minutes and the polishing amount is as small as 5 μm. We were able to manufacture a magnetic disk substrate with extremely excellent flatness.

Example 6 is a CeO with an average particle size of 3 μm and a 90% diameter of 8 μm.₂After performing the pre-polishing treatment using abrasive grains, the same precision polishing treatment as in Example 1 was performed, and by performing the pre-polishing treatment, the surface was superior in a short time as compared with Example 1. A magnetic disk substrate having undulation characteristics was obtained. Also, CeO used for precision polishing₂CeO with a larger particle size than the abrasive grains₂Since the pre-polishing process is performed using abrasive grains, the number of microscopic scratches tends to increase slightly to 3 out of 300 compared to the case where only the precision polishing process is performed, but the yield is 99%. , A fully satisfactory result was obtained.

Then, as is clear from Example 1 and Example 6, if the surface waviness characteristics of the glass base plate are substantially the same, it can be seen that the polishing time can be shortened by performing the pre-polishing treatment.

Example 7 is also CeO which is substantially the same as Example 6.₂After pre-polishing using abrasive grains, precision polishing is performed, but CeO used for precision polishing₂It was found that the abrasive grains have a small average particle size of 0.3 μm and a 90% diameter of 1.2 μm, so that a magnetic disk substrate having extremely good surface waviness characteristics can be obtained in a short time. In addition, the number of microscopic scratches tended to increase slightly to 5 out of 500, but the yield was 99%, which was a sufficiently satisfactory result.

In Example 8, the 90% diameter is 3 μm and the overall particle size is small CeO.₂Pre-polishing treatment is performed using abrasive grains, and precision polishing treatment is performed using fine colloidal silica. Since the particle size is small, the polishing speed is slightly slower and the polishing amount is 70 minutes. Was 10.3 μm, but good surface waviness characteristics could be obtained.

In Example 9, the glass base plate is manufactured by the down draw method, but even when the glass base plate is manufactured by such a down draw method, the surface waviness characteristics are excellent by appropriately controlling the temperature. If a glass base plate can be produced and the surface waviness characteristics are good, a magnetic disk substrate having a desired flatness (waviness characteristics) can be obtained regardless of the method for manufacturing the glass base plate. Do you get it.

As described above, in Examples 1 to 9, by using the glass base plate having excellent surface waviness characteristics, only the precision polishing treatment is performed without performing the rough polishing treatment, or only the pre-polishing treatment and the precision polishing treatment are performed. It is possible to manufacture a magnetic disk substrate having desired surface waviness characteristics and excellent flatness, and since no rough polishing treatment is performed, it is possible to manufacture a magnetic disk substrate with a small amount of polishing and in a short time. I understand. Moreover, it was confirmed that the probability of small scratches occurring was extremely low at 1% or less.

On the other hand, in Comparative Example 1, Al having an average particle size of 5.5 μm and a 90% diameter of 10 μm with respect to a glass base plate obtained from the same production lot as in Example 1.₂O₃Rough polishing is performed using abrasive grains. The surface swell characteristics of the magnetic disk substrate measured after the precision polishing process are as small as 1.0 nm for long wavelength swells and 0.8 nm for medium wavelength swells, but increase to 1.5 nm for short wavelength swells. It is considered that this is because the short wavelength swell was newly formed by the rough polishing treatment. Incidentally, when the surface swell was measured after the rough polishing treatment, the long wavelength swell could be suppressed to 2.5 nm, but the medium wavelength swell and the short wavelength swell were as large as 1.8 nm and 2.2 nm, respectively. It was confirmed that. In addition, micro-scratches were visually confirmed on 72 of the 300 test pieces, and it was found that defective products were manufactured with a probability of 20% or more.

Further, in Comparative Example 2, since the glass base plate obtained from the same production lot as in Example 1 was subjected to the same rough polishing treatment as in Comparative Example 1, new medium-wavelength swells and short-wavelength swells were generated. It is considered to be formed, and therefore it is possible to obtain good surface waviness characteristics as shown in Table 2, but for that purpose, a large amount of polishing of 230 μm must be performed on the substrate surface, and the glass must be polished. It is necessary to form a thick base plate in advance, and a large amount of polishing debris is discharged, which causes an increase in industrial waste.

In Comparative Example 3, a glass base plate having poor surface waviness characteristics is used, and the same rough polishing treatment and precision polishing treatment as in Comparative Example 1 are performed. However, even if a large amount of polishing of 210 μm is performed, the surface waviness characteristics are still obtained. Long-wavelength swells are 1.7 nm, medium-wavelength swells are 1.0 nm, and short-wavelength swells are 1.8 nm, all of which are bad. Moreover, 105 out of 300 micro-scratches are visually confirmed, and 30% of the test pieces have micro-scratches. Beyond.

In Comparative Example 4, a glass base plate obtained from the same production lot as in Comparative Example 3 was used, and the pre-polishing treatment and the precision polishing treatment were performed in the same manner as in Example 6, and the results were good as shown in Table 2. Although it is possible to obtain a magnetic disk substrate having various surface waviness characteristics, since the surface waviness characteristics of the glass base plate are poor, it is necessary to increase the polishing amount to 50 μm in order to obtain such good surface waviness characteristics. In addition, the total polishing time is as long as 100 minutes and lacks mass productivity.

In Comparative Example 5, a glass base plate obtained from the same production lot as in Comparative Example 3 is used, and only the same precision polishing treatment as in Example 1 is performed. Therefore, in order to obtain good surface waviness characteristics, it is necessary to obtain good surface waviness characteristics. It was found that the polishing time was as long as 200 minutes, and the mass productivity was significantly lacking.

[Second Example] Next, the present inventors used each of the test pieces of Example 1 and Comparative Example 1 to form a base layer made of CrMo, a magnetic layer made of CoCrPt, and a protective layer made of hydrogenated carbon by a well-known sputtering method. A magnetic disk was prepared by sequentially stacking it on the surface of the test piece, and a touchdown height test and modulation were measured.

[Touchdown height test] The present inventors conducted a touchdown height test in which the magnetic head was lowered while rotating the magnetic disk, and evaluated the levitation height at which the magnetic head was capable of stable gliding. The touchdown height of the magnetic disk is as high as 11 nm, which may not be able to cope with the low flying height of 10 nm or less, whereas the test piece of Example 1 gives good results with a touchdown height of 5 nm or less, resulting in low flying. It was confirmed that it is suitable for height.

[Measurement of modulation] Modulation M is defined by the mathematical formula (1) when the maximum output of the magnetic disk measured by the oscilloscope is Vmax (mV) and the minimum output is Vmin (mV), and there is little variation in surface unevenness. In order to have good flatness, it is desirable that the modulation M is 8% or less.

M = {(Vmax-Vmin) / (Vmax + Vmin)} × 100 ... (1) However, in the magnetic disk of Comparative Example 1, the modulation M was as large as 10% or more, whereas in the magnetic disk of Example 1, the modulation M was as small as 4% and had good flatness. confirmed.

The substrate for an information recording medium of the present invention and a method for manufacturing the same can be used only for precision polishing using ultrafine abrasive grains having a predetermined particle size, or only for pre-polishing and precision polishing without rough polishing. Since we manufacture substrates for recording media, by using a glass base plate with excellent surface undulations, we can produce substrates for information recording media with excellent surface undulation characteristics in a short time and with a small amount of polishing. It can be obtained and is useful for improving the productivity of the substrate for information recording media. Further, since the substrate for the information recording medium has extremely excellent flatness, it is possible to ensure good followability to the substrate even with a small magnetic head, and the density has been increased today. It can be used as a substrate for a small and large-capacity information recording medium.

Further, since the glass base plate of the present invention is extremely excellent in flatness and flatness, it can be used in various applications requiring high-precision flatness and flatness.