JP5427673B2 - Manufacturing method of glass blank, manufacturing method of magnetic recording medium substrate, and manufacturing method of magnetic recording medium - Google Patents

Description

  The present invention relates to a glass blank manufacturing method, a magnetic recording medium substrate manufacturing method, and a magnetic recording medium manufacturing method.

  Conventionally, to manufacture a magnetic recording medium substrate (magnetic disk substrate) through a press molding process, as described in Patent Document 1, a main surface of a disk-shaped glass blank obtained by press molding is a lapping process. In this method, the flatness is increased to the level required for the substrate, the thickness deviation is reduced, and the main surface is finished by a polishing process (conventional method 1). The polishing process is a process for finishing the main surface to a smooth and defect-free surface, and cannot improve the flatness of the disk main surface and the uniformity of the plate thickness.

  As described in Patent Document 2, the magnetic disk substrate is manufactured by forming a sheet glass by a float method, a downdraw method, or the like, and hollowing out a disk-shaped glass from the sheet glass, drilling a center, and inner and outer circumferences. There is a method (conventional method 2) for performing processing and polishing of the main surface. In this method, a sheet glass having a high flatness can be obtained, so that a wrapping step for improving the flatness and the uniformity of the plate thickness is unnecessary.

  Although the conventional method 1 is superior to the conventional method 2 in terms of the glass utilization rate, a lapping process is indispensable. Therefore, there are problems that a wrapping device is necessary, man-hours are increased, processing time is increased, and processing costs are increased.

JP 2003-54965 A JP 2003-36528 A

  In order to obtain a glass blank capable of omitting the lapping process by the conventional method 1, it is necessary to reduce the plate thickness deviation of the glass blank and increase the flatness. In the conventional method 1, the molten glass flow is flowed out from the glass outlet to the lower mold press molding surface, and the molten glass flow is cut in a state where the lower end is received by the press molding surface. The molten glass lump separated from the molten glass stream is pressed by a lower mold and an upper mold facing the mold, and formed into a thin plate shape.

  The temperature of the lower mold is maintained sufficiently lower than the outflow temperature of the molten glass so that the high-temperature glass is not fused. Therefore, from the time when the molten glass flows out onto the lower mold until the press molding starts, the glass block loses heat from the surface in contact with the lower mold, and the viscosity of the lower surface of the glass block increases locally. . As a result, a glass lump having a large viscosity distribution and temperature distribution is press-molded, and a portion that is difficult to stretch is generated by pressing. Moreover, since the cooling rate after press molding also differs for each part of the press-molded product, the plate thickness deviation increases or the flatness decreases.

  In order to avoid such a situation, the viscosity distribution of the molten glass block just before the start of press molding may be made uniform. For that purpose, the molten glass flow that hangs down from the glass outlet to the air is cut without being held by a member having a lower temperature than the glass such as the lower mold, the molten glass lump is separated and dropped, and the falling molten glass lump is pressed. What is necessary is just to shape | mold.

  However, since there is a difference in the outflow time between the lower end portion and the upper end portion of the molten glass flow depending from the glass outlet, the viscosity of the lower end portion is higher than the viscosity of the upper end portion. Such a viscosity difference reduces the viscosity uniformity in the molten glass lump. In the conventional method 1, such a factor that increases the viscosity distribution of the molten glass lump is hidden in the viscosity distribution caused by the imbalance of the contact time between the glass and the upper and lower molds, and there is no problem.

  The present invention is a glass blank manufacturing method for producing a glass blank for a magnetic recording medium substrate from a molten glass by press molding, in the viscosity distribution of the molten glass lump just before press molding, that is, by uniformizing the temperature distribution, Provided is a method for producing a glass blank for a magnetic recording medium substrate having a small thickness deviation and high flatness, and processing the glass blank produced by the above method into a magnetic recording medium substrate without performing a lapping process It is an object of the present invention to provide a method for manufacturing a magnetic recording medium substrate, and a method for manufacturing a magnetic recording medium using the substrate manufactured by the above method.

The above-mentioned subject is achieved by the following present invention. That is,
The glass blank manufacturing method of the present invention cuts a molten glass stream flowing out from a glass outlet, separates the molten glass lump, and presses the molten glass lump into a disk or a substantially disk-shaped thin glass using a press mold. In a glass blank manufacturing method for producing a glass blank to be molded and processed into a magnetic recording medium substrate, the molten glass flow is cut and melted while the molten glass flow flowing out from the glass outlet is suspended in the air. The glass lump is separated and dropped, and the falling molten glass lump is pressed with a flat press molding surface to form a thin glass, and the vertical direction with respect to the maximum diameter A in the horizontal cross section of the molten glass lump at the time of separation The diameter of the glass outlet is determined so that the ratio B / A of the length B is in the range of 0.5 to 5, and the outflow viscosity of the molten glass is 500 to 1050d. And controlling the outflow temperature of the molten glass so as to be constant in the range of a · s.

In addition, in the glass blank manufacturing method of the present invention, the height difference from the cutting position of the molten glass flow to the center of the press molding surface of the press mold is set to 1000 mm or less .

In another embodiment of the method for producing a glass blank of the present invention, the glass component is expressed in terms of mol% in terms of a mol%, and SiO ₂ is 50 to 75%, Al ₂ O ₃ is 1 to 15%, LiO _2. 12 to 35% in total of at least one component selected from Na ₂ O and K ₂ O, and 0 to 20% in total of at least one component selected from MgO, CaO, SrO, BaO and ZnO , and _{ZrO 2, TiO 2, La 2} O 3, Y 2 O 3, Ta 2 O 5, Nb 2 O 5 and 0-10% in total of at least one component selected from HfO _2, a glass containing It is preferable to press-mold the thin glass sheet.

  In another embodiment of the method for producing a glass blank of the present invention, it is preferable to press-mold a thin glass plate made of glass to which 0.1 to 3.5% by mass of Ce oxide is added in addition to the glass component. .

  In another embodiment of the glass blank manufacturing method of the present invention, Sn oxide and Ce oxide are added in addition to the glass component, and the total amount of Sn oxide and Ce oxide added is 0.1 to 3. 5 mass%, the mass ratio of the addition amount of Sn oxide to the total addition amount of Sn oxide and Ce oxide (addition amount of Sn oxide / (addition amount of Sn oxide + addition amount of Ce oxide)) is 0 It is preferable to press-mold a thin glass plate made of .01-0.99 glass.

  The method for producing a magnetic recording medium substrate of the present invention is characterized in that the magnetic recording medium substrate is produced through at least a polishing step of polishing the main surface of the glass blank produced by the method for producing a glass blank of the present invention. .

  The method for producing a magnetic recording medium of the present invention comprises at least a magnetic recording layer forming step of forming a magnetic recording layer on a magnetic recording medium substrate produced by the method for producing a magnetic recording medium substrate of the present invention. It is characterized by manufacturing.

  According to the present invention, a molten glass is press-molded, and a glass blank having a small flat thickness deviation and a high flatness, that is, a magnetic recording medium substrate having a required flat thickness deviation and flatness even if the lapping step is omitted. The manufacturing method of the glass blank which makes it possible to obtain is provided. As a result, lapping can be omitted in the substrate manufacturing process, and the productivity of the magnetic recording medium substrate and the magnetic recording medium can be increased.

The state which cut | disconnects the molten glass flow which flows out from a glass outflow port when it sees from a horizontal direction using a shear blade is shown. The mode which cut | disconnects a molten glass flow and isolate | separates a molten glass lump is shown. The state which the separated molten glass lump falls is shown. A mode that a molten glass lump falls between the press molding surfaces which oppose is shown. The press mold which shows the mode of a press start of a molten glass lump, and the perpendicular | vertical cross section of a molten glass lump are shown. 2 is a vertical cross section of a press mold and glass showing a process of stretching glass into a thin plate shape by pressing. 2 shows a vertical cross section of a press mold and a thin glass when it is formed into a thin glass by a press. It is a vertical sectional view of a press mold and a thin glass showing how the thin glass is cooled while the press molding surface follows the thin glass. It is a vertical sectional view which shows a mode that thin glass is released from one side of a press molding surface. The state which takes out thin glass from a press-molding die is shown. The molten glass flow hanging down from the glass outlet is cut by a shear blade to obtain a molten glass lump.

[Glass blank manufacturing method]
The manufacturing method of the glass blank of this embodiment cuts the molten glass flow flowing out from the glass outlet and separates the molten glass lump, and the molten glass lump is formed into a disk or a substantially disk-shaped thin plate using a press mold. In a glass blank manufacturing method for producing a glass blank that is press-molded into glass and processed into a substrate for a magnetic recording medium, the molten glass flow is cut in a state where the molten glass flow flowing out from the glass outlet is suspended in the air. The molten glass lump is separated and dropped, and the falling molten glass lump is pressed with a flat press-molded surface to be formed into a thin glass, and the maximum diameter A in the horizontal section of the molten glass lump at the time of separation is The diameter of the glass outlet is determined so that the ratio B / A of the length B in the vertical direction is in the range of 0.5 to 5, and the outflow viscosity of the molten glass is 500 to 1. And controlling the outflow temperature of the molten glass so as to be constant in the range of 50dPa · s.

  Hereinafter, an embodiment of the glass blank manufacturing method of the present embodiment will be described with reference to the drawings. In FIG. 1, a molten glass stream 2 flowing out from a glass outlet opening at the lower end of a glass outlet pipe 1 is suspended in the air. The cutting of the molten glass stream 2 is performed by crossing the tips of the pair of shear blades 3-1 and 3-2 and shearing the glass. The outflow viscosity of the molten glass is controlled to be constant in the range of 500 dPa · s to 1050 dPa · s by adjusting the temperature of the glass outflow tube 1.

  FIG. 2 shows the state of the moment when the tips of the shear blades 3-1 and 3-2 are crossed so that there is no gap, the lower part of the molten glass flow 2 is cut, and the molten glass lump 4 is separated. . FIG. 3 shows how the separated molten glass lump falls. FIG. 4 shows a vertical cross section of the press molds 5 and 6.

  The press mold 5 is attached around a press mold body 5-1 having a press mold surface 5-1-a and the press mold body 5-1, and the space between the press mold surfaces is made of thin glass during press molding. When the press mold body 5-1 is brought into contact with the press mold 6 so as to be equal to the plate thickness to determine the interval between the press mold surfaces and the main surface of the thin glass is followed by the press mold body 5-1. 1 is constituted by a guide member 5-2 for guiding 1.

  The material constituting the press mold is preferably a metal or an alloy in consideration of heat resistance, workability, and durability. Among them, a metal or alloy having a heat resistant temperature of 1000 ° C. or higher, preferably 1100 ° C. or higher, when used as a press mold is more preferable. Specifically, spheroidal graphite cast iron (FCD), alloy tool steel (SKD61 etc.), high speed steel (SKH), cemented carbide, colmonoy, stellite, etc. are preferable.

  Since the press molding surface is transferred to glass and the main surface of the glass blank is formed, the surface roughness of the press molding surface and the surface roughness of the glass blank main surface are substantially equal. Since the surface roughness of the glass blank main surface is preferably in the range of 0.01 to 10 μm in performing scribing and grinding using a diamond sheet, which will be described later, the surface roughness of the press-molded surface is also 0. A range of 01 to 10 μm is preferred.

  The press mold 6 is attached around the press mold main body 6-1 having the press mold surface 6-1-a and the press mold main body 6-1, and the distance between the press mold surfaces at the time of press molding is thin glass. The press mold body 6 is brought into contact with the press mold 5 so as to be equal to the plate thickness to determine the interval between the press mold surfaces, and when the press mold body 6-1 follows the main surface of the thin glass. 1 is constituted by a guide member 6-2 for guiding 1.

  In FIG. 4, in order to press the molten glass lump 4, the molten glass lump 4 falls between the press molds 5 and 6 being driven forward. FIG. 5 shows a moment when the molten glass lump 4 is started to be pressed by the press molding surfaces 5-1-a and 6-1-a.

  The fall distance of the molten glass lump 4 is adjusted. The drop distance is preferably 1000 mm or less so that the viscosity of the molten glass lump does not increase and does not deviate from the viscosity range suitable for press molding, and the drop speed does not increase and the position of the press does not fluctuate. , 500 mm or less, more preferably 300 mm or less, and even more preferably 200 mm or less.

  When the surface of the molten glass block comes into contact with the press molding surface, it is solidified so as to stick to the press molding surface. When the press is advanced, the glass is spread with a uniform thickness around the position where the molten glass lump and the press molding surface first contact each other, and is formed into a disk-like or substantially disk-like thin plate glass.

  FIG. 6 shows how the glass is spread out during the pressing process. FIG. 7 shows the press molding surface 5-1-a and the press molding surface by bringing the abutting surface 5-1-a of the guide member 5-1 into contact with the abutting surface 6-1-a of the guide member 6-1. The state which prescribed | regulated the space | interval of 6-1-a to the distance corresponded to the plate | board thickness of a glass blank is shown. The contact between the contact surface 5-1-a and the contact surface 6-1-a also serves to maintain the parallel state between the press molding surface 5-1-a and the press molding surface 6-1-a. The time from the start of pressing shown in FIG. 5 to the closing of the mold shown in FIG. 7 is preferably within 0.1 seconds for thinning the molten glass lump.

  In FIG. 8, the press molding surfaces 5-1-a and 6-1-a are main surfaces of thin glass in a state where the contact surface 5-1-a and the contact surface 6-1 a are in contact with each other. A pressure sufficiently smaller than the press pressure is applied to the press mold main bodies 5-1 and 6-1 so as to maintain the state in close contact with the press. If the press pressure is increased in this state, the glass may be damaged. This state is continued for a few seconds to cool the thin glass.

  Next, as shown in FIG. 9, the press molds 5 and 6 are moved backward to release the thin glass 4-B from the press molding surface 6-1-a. Next, as shown in FIG. 10, the thin glass plate 4-B is released from the press-molded surface 5-1-a and taken out. When releasing the thin glass 4-B from the press molding surface 5-1-a, without applying a large force to the thin glass, if the mold is released so as to peel off the thin glass by applying a force from the outer peripheral direction of the thin glass. Then, it can be removed from the press mold.

  The plate thickness and diameter (arithmetic mean of the major axis and minor axis) of the glass blank can be appropriately set by adjusting the amount of molten glass lump and the distance between the opposing press molding surfaces during press molding. There are no particular limitations on the glass blank plate thickness setting range and the arithmetic mean of the major axis and minor axis (referred to as outer diameter), but the thickness and outer diameter of the magnetic recording medium substrate to be manufactured should be processed. A glass blank having a plate thickness and diameter to which is added is formed. The thickness of a typical glass blank is 0.75 to 1.1 mm, the outer diameter is 75 to 80 mm, the outer diameter / thickness ratio is 50 to 150, and the roundness is ± 0. Within 5 mm.

  The temperature of the press mold may be set to a temperature that is sufficiently lower than the temperature of the molten glass and that does not hinder the elongation of the glass when the thin glass is formed in order to prevent fusion of the molten glass. With the start of press molding, the viscosity of the portion in contact with the press-molded surface of the glass rises rapidly, but the viscosity inside the glass is low. When the press molding speed is slowed down, the viscosity rises due to the temperature drop inside the glass, and it becomes difficult to stretch the glass thinly so that the outer diameter / plate thickness ratio becomes the above. Therefore, it is preferable that the time from the start of pressing the glass to the interval between the opposing press-molding surfaces to be the thickness of the glass blank is within 0.1 seconds, and more preferably within 0.08 seconds.

  In order to reduce the thickness deviation of the glass blank and improve the flatness, the viscosity distribution of the molten glass lump immediately before the start of pressing is made uniform so that the molten glass lump does not have a portion that is easily stretched and a portion that is difficult to stretch. It is desirable to do. For that purpose, the molten glass flow drooping in the air from the glass outlet is cut, and the molten glass below the cut portion is separated. Since the molten glass flow that hangs down from the glass outlet is surrounded by a highly heat-insulating gas, such as the atmosphere, a local temperature drop as in the conventional method 1 can be avoided.

  Further, in order to reduce the viscosity distribution of the molten glass block due to the difference in the flow time of the molten glass, the ratio B / A of the length B in the vertical direction to the maximum diameter A in the horizontal section of the molten glass block at the time of separation is 0.5. The diameter of the glass outlet and the outflow viscosity of the molten glass are controlled so as to be constant in the range of ˜5.

  FIG. 11 is a schematic cross-sectional view showing a state in which a molten glass flow hanging from the glass outlet is cut by a shear blade to obtain a molten glass lump. Here, in FIG. 11, reference signs A and B mean the maximum diameter and the vertical length of the horizontal section of the molten glass mass 4 separated from the molten glass stream 2, respectively. 11A to 11C show a process in which a molten glass lump 4 having a ratio B / A of about 1 is formed, and is shown in the lower part of FIG. (F) to (F) show a process in which a molten glass lump 4 having a ratio B / A sufficiently smaller than 1 is formed. In FIG. 11, (A) and (D) show the state before separating the molten glass lump 4 from the molten glass stream 2, and (B) and (E) show the molten glass lump 2 from the molten glass stream 2. 4 shows a state in the middle of separation, and (C) and (F) show a state immediately after separating the molten glass lump 4 from the molten glass stream 2. In addition, the horizontal cross section of the molten glass block at the time of separation usually tends to be a circle due to surface tension. For this reason, when the horizontal cross-sectional shape of the molten glass flow 2 is a circle, A is the diameter of the horizontal cross-section, and when it is an ellipse, the long diameter is A. Here, the ratio B / A is 0.5 to 5 by appropriately setting the inner diameter of the glass outflow pipe 1, the viscosity (temperature) of the molten glass flow 2, and the outflow amount per unit time of the molten glass flow 2. Can be adjusted within the range. The outflow amount per unit time of the molten glass flow can be adjusted by the diameter of the glass outflow tube and the outflow viscosity of the molten glass flow.

  When the ratio B / A exceeds 5, the difference in viscosity between the upper end portion and the lower end portion of the molten glass lump increases, and it becomes difficult to spread the glass evenly by press molding. As a result, the thickness deviation of the glass blank increases and the flatness also decreases.

  When the ratio B / A is less than 0.5, the diameter of the glass outlet becomes large and the molten glass flow becomes thick. As a result, cutting marks called “shear marks” generated when cutting the molten glass are increased, and the amount of processing for removing the shear marks is increased. When the molten glass stream is cut one after another to obtain a molten glass lump, the cutting site can be at the top and bottom of the glass lump, but the lower cutting part is the hot glass around it until the upper cut is made However, although the shear mark disappears, the upper cut part has a short time from the separation of the molten glass lump to the press molding, and thus the viscosity is not lowered by such reheating. Therefore, if the ratio B / A is too small, the viscosity distribution of the molten glass lump becomes large. Further, if the diameter of the glass outlet is excessively large, it becomes difficult to control the outflow of the molten glass.

  Thus, the ratio B / A is related to the viscosity distribution of the molten glass lump, and the viscosity distribution of the molten glass lump affects the thickness deviation and flatness of the glass blank. You may adjust in relation to thickness deviation and flatness.

  The preferred lower limit of the ratio B / A is 0.8, the more preferred lower limit is 0.9, the still more preferred lower limit is 0.95, and the still more preferred lower limit is 1.0. On the other hand, the preferable upper limit of the ratio B / A is 4.5, the more preferable upper limit is 4, the still more preferable upper limit is 3.5, the still more preferable upper limit is 3, the still more preferable upper limit is 2.5, and the still more preferable upper limit is 2. is there.

  The diameter of the glass outlet affects the maximum diameter A in the horizontal cross section of the molten glass lump immediately after the separation and the mass of the molten glass that can be suspended at the glass outlet. Therefore, the diameter of the glass outlet is determined so that the ratio B / A can be adjusted within the above range.

  When the outflow viscosity of the molten glass is less than 500 dPa · s, it becomes difficult to suspend the molten glass flow necessary for obtaining a molten glass mass having a ratio B / A in the above range. On the other hand, when the outflow viscosity of the molten glass exceeds 1050 dPa · s, it becomes difficult to press-mold thin glass having a uniform thickness. Therefore, the outflow viscosity of the molten glass is in the range of 500 to 1050 dPa · s, and the outflow viscosity of the molten glass is set in order to stably produce a glass blank having a constant diameter, plate thickness, plate thickness deviation, and flatness. Control the temperature to be constant.

In this way, a molten glass lump having a viscosity capable of being thinned and having a uniform viscosity distribution is obtained, and the molten glass lump is dropped, and a press mold having flat press molding surfaces facing each other in parallel is obtained. Use to mold into thin glass.

  By using a pair of press molds having a flat press molding surface and facing the press molds so that the press molding surfaces are parallel to each other, the molten glass lump having a uniform viscosity distribution is press molded. A glass blank having a thickness deviation of 10 μm or less and a flatness of 10 μm or less can be produced.

  When the timing of dropping the molten glass lump is shifted from the timing of pressing, the position where the molten glass lump is pressed changes. Since the speed at which the molten glass lump falls into the space between the press molding surfaces reaches several meters per second, the time difference due to the timing shift causes the press position to fluctuate. If the press molding surface is not a flat surface, the main surface shape of the glass blank also fluctuates due to variations in the press position, making it difficult to stably produce a glass blank having the required shape accuracy.

  According to the preferable aspect of the manufacturing method of the glass blank of this embodiment, a press position is fluctuate | varied by making a pair of opposing press molding surfaces into a flat surface, and making it wider than the main surface of the glass blank to be shape | molded. In addition, a glass blank having a required shape accuracy can be produced stably. In addition, the preferable range of the flatness of the glass blank is within 8 μm, the more preferable range is within 6 μm, and the further preferable range is within 4 μm.

  In order to make the outflow viscosity of the molten glass constant within a predetermined range, the temperature of the molten glass is controlled. The temperature control of the molten glass can be performed by adjusting the degree of heating of the glass outflow tube. For example, when using an outflow pipe made of a metal such as platinum or an alloy, Joule heat is generated by passing an electric current through the outflow pipe, and the temperature of the molten glass flowing in the glass outflow pipe is controlled by controlling the electric current. Control. Alternatively, a high-frequency coil is disposed around the glass outflow tube, the glass outflow tube is induction-heated at high frequency, and the high-frequency current flowing through the coil is controlled to control the temperature of the molten glass flowing through the glass outflow tube.

  From the viewpoint of reducing the thickness deviation of the glass blank and improving the flatness, a preferable range of the outflow viscosity of the molten glass is 600 to 900 dPa · s.

  The material constituting the press mold is preferably a metal or an alloy in consideration of heat resistance, workability, and durability. Among them, a metal or alloy having a heat resistant temperature of 1000 ° C. or higher, preferably 1100 ° C. or higher, when used as a press mold is more preferable. Specifically, spheroidal graphite cast iron (FCD), alloy tool steel (SKD61 etc.), high speed steel (SKH), cemented carbide, colmonoy, stellite, etc. are preferable.

  The heat-resistant temperature of the material is about 1250 ° C. In order to suppress thermal deterioration of the press mold and avoid devitrification of the glass, it is desirable to use glass having a liquidus temperature of 1250 ° C. or lower.

In addition to forming a glass blank with a small plate thickness deviation and excellent flatness, it also achieves glass meltability, devitrification resistance, chemical durability, rigidity, high thermal expansion characteristics, etc. required for a magnetic recording medium substrate The preferred glass is converted to oxide standard and expressed in mol%.
The SiO ₂ 50~75%,
1 to 15% of Al ₂ O ₃ ,
LiO _2, 12 to 35% in total of at least one component selected from Na ₂ O and _{K 2} O,
0-20% in total of at least one component selected from MgO, CaO, SrO, BaO and ZnO, and
It is a glass containing 0 to 10% in total of at least one component selected from ZrO ₂ , TiO ₂ , La ₂ O ₃ , Y ₂ O ₃ , Ta ₂ O ₅ , Nb ₂ O ₅ and HfO ₂ .

SiO ₂ is a glass network-forming component and an essential component that functions to improve glass stability, chemical durability, and particularly acid resistance. If the content of SiO ₂ is less than 50%, the above function cannot be obtained sufficiently, and if it exceeds 75%, undissolved matter is generated in the glass, or the viscosity of the glass at the time of clarification becomes too high, and the bubbles are blown out. It becomes insufficient. Therefore, the content of SiO ₂ is preferably 50 to 75%. A more preferable range of the content of SiO ₂ is 60 to 75%.

Al ₂ O ₃ also contributes to the formation of a glass network, and functions to improve glass stability and chemical durability. When chemically strengthened, Al ₂ O ₃ also functions to increase the ion exchange rate during chemical strengthening. If the content of Al ₂ O ₃ is less than 1%, it is difficult to obtain the above effect, and if the content of Al ₂ O ₃ exceeds 15%, the melting property of the glass is lowered and undissolved substances are likely to be generated. . In addition, the thermal expansion coefficient decreases and the Young's modulus also decreases. Therefore, the content of Al ₂ O ₃ is preferably 1 to 15%. A preferable range of the content of Al ₂ O ₃ is 5 to 14%.

LiO ₂ , Na ₂ O and K ₂ O serve to improve the meltability and moldability of the glass. It also serves to increase the coefficient of thermal expansion. If the content of LiO ₂ , Na ₂ O and K ₂ O is less than 12%, the above function cannot be obtained sufficiently, and if it exceeds 35%, chemical durability, particularly acid resistance is reduced, Thermal stability is reduced. Further, the glass transition temperature is lowered and the heat resistance is also lowered. Accordingly, the content of _LiO 2, Na ₂ O and _{K 2} O is preferably 12 to 35%. More preferred range of the content of LiO _2, Na ₂ O and _{K 2} O is 15-25%. Of the _LiO 2, Na ₂ O and _{K 2} O, those functions to lower the glass transition temperature is largest is LiO _2.

  MgO, CaO, SrO, BaO, and ZnO function to improve the meltability, moldability, and Young's modulus of glass. It also functions to increase the thermal expansion coefficient and Young's modulus. However, when the total content of MgO, CaO, SrO, BaO and ZnO exceeds 20%, chemical durability and thermal stability of the glass are lowered. Therefore, the total content of MgO, CaO, SrO, BaO and ZnO is preferably 0 to 20%. A more preferable range of the total content of MgO, CaO, SrO, BaO and ZnO is 1 to 6%.

ZrO ₂ , TiO ₂ , La ₂ O ₃ , Y ₂ O ₃ , Ta ₂ O ₅ , Nb ₂ O _5, and HfO ₂ improve chemical durability, especially alkali resistance, increase glass transition temperature, and heat resistance Improves the Young's modulus and fracture toughness. However, if the total content of ZrO ₂ , TiO ₂ , La ₂ O ₃ , Y ₂ O ₃ , Ta ₂ O ₅ , Nb ₂ O ₅ and HfO ₂ exceeds 10%, the melting property of the glass is lowered and This leaves undissolved glass raw materials. Therefore, the total content of ZrO ₂ , TiO ₂ , La ₂ O ₃ , Y ₂ O ₃ , Ta ₂ O ₅ , Nb ₂ O ₅ and HfO ₂ is preferably 0 to 10%. A more preferable range of the total content of ZrO ₂ , TiO ₂ , La ₂ O ₃ , Y ₂ O ₃ , Ta ₂ O ₅ , Nb ₂ O ₅ and HfO ₂ is 1 to 9%.

  In order to promote the bubble breakage of the molten glass, including the glass, a glass blank can be formed using a glass component and 0.1 to 3.5% by mass of Ce oxide added on an external basis. preferable.

  It is considered that the heat radiation from the molten glass that has flowed out is mostly due to thermal radiation. Ce emits light in high-temperature glass and has an action of promoting thermal radiation. As a result, the thermal energy of the glass tends to be dissipated, and the temperature difference between the upstream and downstream of the molten glass flow due to the difference in outflow time tends to increase.

  Thus, even if the glass is susceptible to a temperature difference, according to the glass blank manufacturing method of the present embodiment, after selecting the diameter of the glass outlet, by controlling the outflow temperature of the molten glass, A glass blank having a small thickness deviation and excellent flatness can be produced.

  In order to further enhance the clarification effect of the glass due to the addition of Ce oxide, Sn oxide and Ce oxide are added in addition to the glass component, and the total amount of Sn oxide and Ce oxide added is 0. 0.1-3.5 mass%, mass ratio of Sn oxide addition amount to total addition amount of Sn oxide and Ce oxide (addition amount of Sn oxide / (addition amount of Sn oxide + addition of Ce oxide) The amount)) is preferably 0.01 to 0.99.

  Each said glass is obtained by melt | dissolving a glass raw material, clarifying and homogenizing the obtained molten glass, and then rapidly cooling, ie, flowing out and shape | molding a molten glass. The process of refining the molten glass is performed at a relatively high temperature, and the homogenization process is performed at a relatively low temperature. In the clarification step, bubbles are actively generated in the glass, and the fine bubbles contained in the glass are taken into large bubbles to make it easier to rise. On the other hand, in the state where the temperature of the glass is lowered toward the outflow, it is desirable to eliminate the bubbles by incorporating oxygen present as a gas in the glass as a glass component. Both Sn and Ce have a function of releasing and taking in gas, but Sn has a strong function of promoting clarification by actively releasing oxygen mainly in a high temperature state (temperature range of about 1400 to 16000 C), and Ce is low in temperature. It has a strong function of taking oxygen in a state (temperature range of about 1200 to 14000 C) and fixing it as a glass component. By coexisting Sn and Ce exhibiting an excellent clarification action in different temperature regions in this way, sufficient foaming can be achieved even in glasses with limited Sb, As, and F.

[Method of manufacturing magnetic recording medium substrate]
The method for manufacturing a magnetic recording medium substrate according to this embodiment is characterized in that the magnetic recording medium substrate is manufactured through at least a polishing step for polishing the main surface of the glass blank produced by the method for manufacturing a glass blank according to this embodiment. And

  First, scribing is performed on a glass blank obtained by press molding. Scribe is a glass blank that is cut into two concentric circles (inner concentric circle and outer concentric circle) with a scriber made of super steel alloy or diamond particles on the surface of the glass blank in order to make the molded glass blank into a ring shape of a predetermined size. This refers to providing a line (linear scratch). The glass blank scribed in two concentric shapes is partially heated and the outer portion of the outer concentric circle is removed due to the difference in thermal expansion of the glass. As a result, a perfect circular disk-shaped glass is obtained.

  Since the roughness of the main surface of a glass blank is 0.01 micrometer or less, a cutting line can be suitably provided using a scriber. In addition, when the roughness of the main surface of a glass blank exceeds 1 micrometer, since a scriber does not follow surface unevenness and a cutting line cannot be provided uniformly, scribing is performed after the main surface is smoothed.

  Next, shape processing of the scribed glass is performed. Shape processing includes chamfering (chamfering of the outer peripheral end and the inner peripheral end). In chamfering, chamfering is performed on the outer peripheral end and inner peripheral end of the ring-shaped glass with a diamond grindstone.

  Next, the end surface of the disk-shaped glass is polished. In the end surface polishing, the inner peripheral side end surface and the outer peripheral side end surface of the glass are mirror-finished by brush polishing. At this time, a slurry containing fine particles such as cerium oxide as free abrasive grains is used. Preventing the occurrence of ion precipitation that causes corrosion such as sodium and potassium by removing contamination such as dirt, damage or scratches attached to the end surface of the glass by end face polishing Can do.

  Next, 1st grinding | polishing is given to the main surface of disk-shaped glass. The first polishing is intended to remove scratches and distortions remaining on the main surface. The machining allowance by the first polishing is, for example, about several μm to 10 μm. Since it is not necessary to perform a grinding process with a large machining allowance, the glass is not scratched or distorted due to the grinding process. Therefore, the machining allowance in the first polishing process is small.

  In the first polishing step and the second polishing step described later, a double-side polishing apparatus is used. The double-side polishing apparatus is an apparatus that performs polishing by using a polishing pad and relatively moving a disk-shaped glass and a polishing pad. The double-side polishing apparatus includes a polishing carrier mounting portion having an internal gear and a sun gear that are driven to rotate at a predetermined rotation ratio, and an upper surface plate and a lower surface plate that are driven to rotate reversely with respect to the polishing carrier mounting portion. Have A polishing pad, which will be described later, is attached to the surfaces of the upper and lower surface plates facing the disk-shaped glass. The polishing carrier mounted so as to mesh with the internal gear and the sun gear revolves around the sun gear while rotating around the sun gear.

  Each of the polishing carriers holds a plurality of disc-shaped glasses. The upper surface plate is movable in the vertical direction, and presses the polishing pad against the main surfaces of the front and back surfaces of the disk-shaped glass. Then, while supplying a slurry (polishing liquid) containing abrasive grains (polishing material), the planetary gear motion of the polishing carrier and the upper surface plate and the lower surface plate rotate reversely to each other, so that the disk-shaped glass and the polishing pad The main surfaces of the front and back surfaces of the disk-shaped glass are polished. In the first polishing step, for example, a hard resin polisher is used as the polishing pad, and for example, cerium oxide abrasive is used as the polishing material.

Next, the disk-shaped glass after the first polishing is chemically strengthened. When the glass contains Li ₂ O or Na ₂ O as the chemical strengthening solution, for example, a mixed solution of potassium nitrate (60%) and sodium nitrate (40%) can be used. In chemical strengthening, the chemical strengthening liquid is heated to, for example, 300 ° C. to 400 ° C. and the cleaned glass is preheated to, for example, 200 ° C. to 300 ° C., and then the glass is placed in the chemical strengthening liquid, for example, 3 hours to 4 hours. Soaked. The immersion is preferably performed in a state of being housed in a holder so that a plurality of glasses are held at the end faces so that both main surfaces of the glass are chemically strengthened. In the case of Li ₂ O-free glass, the chemical strengthening solution is preferably a molten salt of potassium nitrate.

  Thus, by immersing the glass in the chemical strengthening solution, lithium ions and sodium ions on the surface layer of the glass are replaced with sodium ions and potassium ions having relatively large ionic radii in the chemical strengthening solution, respectively. A compressive stress layer with a thickness of ˜200 μm is formed. As a result, the glass is strengthened and has good impact resistance. Note that the chemically strengthened glass is washed. For example, after washing with sulfuric acid, washing with pure water, IPA (isopropyl alcohol), or the like.

  Next, second polishing is performed on the chemically strengthened and sufficiently cleaned glass. The machining allowance by the second polishing is, for example, about 1 μm. The second polishing is intended to finish the main surface into a mirror surface. In the second polishing step, as with the first polishing step, the disc-shaped glass is polished using a double-side polishing apparatus. The polishing abrasive grains contained in the polishing liquid (slurry) to be used and the composition of the polishing pad Is different. In the second polishing step, the grain size of the abrasive grains to be used is made smaller than in the first polishing step, and the hardness of the polishing pad is made softer. For example, in the second polishing process, for example, a soft foamed resin polisher is used as the polishing pad, and as the abrasive, for example, cerium oxide abrasive grains finer than the cerium oxide abrasive grains used in the first polishing process are used.

  The disk-shaped glass polished in the second polishing process is washed again. In cleaning, a neutral detergent, pure water, and IPA are used. By the second polishing, a magnetic disk glass substrate having a main surface flatness of 4 μm or less and a main surface roughness of 0.2 nm or less is obtained. Thereafter, each layer such as a magnetic layer is formed on the glass substrate for magnetic disk to produce a magnetic disk.

  In addition, although a chemical strengthening process is performed between a 1st grinding | polishing process and a 2nd grinding | polishing process, it is not limited to this order. As long as a 2nd grinding | polishing process is performed after a 1st grinding | polishing process, a chemical strengthening process can be arrange | positioned suitably. For example, the order of the first polishing process → the second polishing process → the chemical strengthening process (hereinafter, process order 1) may be used. However, in the process order 1, since the surface unevenness that may be generated by the chemical strengthening process is not removed, the process order of the first polishing process → the chemical strengthening process → the second polishing process is more preferable.

[Method of manufacturing magnetic recording medium]
The method for manufacturing a magnetic recording medium according to the present embodiment includes at least a magnetic recording layer forming step for forming a magnetic recording layer on the magnetic recording medium substrate manufactured by the method for manufacturing a magnetic recording medium substrate according to the present embodiment. A medium is manufactured.

  A magnetic recording medium substrate (magnetic disk) is produced by depositing a layer such as a magnetic layer on the main surface of the magnetic recording medium substrate (magnetic disk glass substrate) produced by the method described above. For example, an adhesion layer, a soft magnetic layer, a nonmagnetic underlayer, a perpendicular magnetic recording layer, a protective layer, and a lubricating layer are sequentially laminated from the main surface side of the substrate. For example, a Cr alloy is used for the adhesion layer, and functions as an adhesion layer with the glass substrate. For example, a CoTaZr alloy or the like is used for the soft magnetic layer, a granular nonmagnetic layer or the like is used for the nonmagnetic underlayer, and a granular magnetic layer or the like is used for the perpendicular magnetic recording layer. In addition, a material made of hydrogen carbon is used for the protective layer, and a fluorine resin or the like is used for the lubricating layer, for example.

More specifically, an in-line sputtering apparatus is used on the glass substrate, and CrTi adhesion layer, CoTaZr / Ru / CoTaZr soft magnetic layer, and CoCrSiO ₂ nonmagnetic granular layer are formed on both main surfaces of the glass substrate. A base layer, a CoCrPt—SiO ₂ · TiO ₂ granular magnetic layer, and a hydrogenated carbon protective film are sequentially formed. Further, a perfluoropolyether lubricating layer is formed on the formed uppermost layer by a dip method to obtain a magnetic recording medium (magnetic disk).

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to a following example.

Example 1
Raw materials such as oxides, carbonates, nitrates, and hydroxides were weighed so as to obtain the five types of glasses (No. 1 to No. 4) shown in Table 1, and mixed well to obtain a blended raw material. This raw material is put into a melting tank in a glass melting furnace, heated and melted, the obtained molten glass is flowed from the melting tank to the clarification tank, defoamed in the clarification tank, and further poured into the work tank. The mixture was stirred and homogenized in the work tank, and flowed out of the glass outflow pipe attached to the bottom of the work tank. The temperature of the melting tank, clarification tank, work tank, and glass outflow pipe is controlled, and the temperature and viscosity of the glass are maintained in the optimum state in each step.

The molten glass flowing out from the glass outflow pipe was cast into a mold. The glass transition temperature and the liquidus temperature were measured using the obtained glass as a sample. The measuring method of glass transition temperature and liquidus temperature is shown below.
(1) Glass transition temperature Tg
The glass transition temperature Tg of each glass was measured using a thermomechanical analyzer (TMA).
(2) Liquid phase temperature Put a glass sample in a platinum crucible, hold it at a predetermined temperature for 2 hours, take it out of the furnace, cool it, observe the presence or absence of crystal precipitation with a microscope, and set the minimum temperature at which no crystal is observed to the liquid phase temperature. (LT).
Table 1 shows the glass transition temperature and liquidus temperature of each glass.

  Glass blanks were sequentially produced using these four types of glasses. The glass blank is produced by the method shown in FIGS.

  The flow viscosity of the molten glass is adjusted to be constant in the range of 600 to 900 dPa · s, the diameter of the glass outlet is adjusted in the range of φ13 mm to φ17 mm, and the ratio B / A of the molten glass lump ratio at the time of separation is adjusted. The press molding was carried out at the respective ratios of 4.5, 3, 2, and 1. The ratio B / A is obtained from the size on the image obtained by photographing the molten glass block at the time of separation with a high-speed camera. The press mold main bodies 5-1, 6-1 and the guide members 5-1, 6-1 were made of cast iron (FCD).

  The height of the press mold was adjusted so that the falling distance from when the molten glass lump was separated until it was pressed was within 200 mm. The time from the start of pressing to closing the mold was set to within 0.1 seconds, and the pressing pressure was set to about 6.7 MPa. Next, the pressure is reduced and the glass is cooled while maintaining the state where both press-formed surfaces are in close contact with the glass for about several seconds. Next, the press pressure is released, the press mold is retracted, the glass blank is released and removed. In the series of steps described above, the press mold may be cooled using a cooling medium to suppress the temperature rise.

  The diameter (arithmetic mean of major axis and minor axis), plate thickness, plate thickness deviation, and flatness of the obtained glass blank were measured using a three-dimensional measuring instrument and a micrometer. The resulting glass blank had a diameter of 70 to 78 mm, a plate thickness of 0.90 mm, a plate thickness deviation of 10 μm or less, and a flatness of 4 μm or less. When the ratio B / A is in the range of 1 to 3, the major axis / minor axis ratio falls within the range of 1 to 1.1.

(Comparative example)
When the ratio B / A exceeded 5, the plate thickness deviation and the flatness deteriorated. On the other hand, when the ratio B / A was smaller than 0.5, the thickness deviation and the flatness deteriorated rapidly. The glass blank is annealed to reduce and remove strain.

(Example 2)
Using the glass blank produced in Example 1, a scribing process was performed on the part that becomes the outer periphery of the magnetic disk substrate and the part that becomes the central hole. By such processing, two concentric grooves are formed on the outer side and the outer side. Next, the scribed portion is partially heated to generate a crack along the scribed groove due to the difference in thermal expansion of the glass, and the outer and inner portions of the outer concentric circle are removed. As a result, a perfect circular disk-shaped glass is obtained. By this processing, the trace of the shea mark is completely removed.

  Next, the shape of the disk-shaped glass was processed by chamfering or the like, and end face polishing was further performed. Next, after subjecting the main surface of the disk-shaped glass to the first polishing, the glass is immersed in a chemical strengthening solution and chemically strengthened. After chemical strengthening, the glass that was sufficiently washed was subjected to the second polishing. After the second polishing step, the disk-shaped glass was washed again to produce a magnetic disk glass substrate. The substrate has an outer diameter of 65 mm, a center hole diameter of 20 mm, a thickness of 0.8 mm, a main surface flatness of 4 μm or less, and a main surface roughness of 0.2 nm or less. A recording medium substrate could be obtained.

(Example 3)
On both main surfaces of the magnetic recording medium substrate (magnetic disk glass substrate) produced in Example 2, an in-line sputtering apparatus was used to sequentially deposit a CrTi adhesion layer, a CoTaZr / Ru / CoTaZr soft magnetic layer, and CoCrSiO. ₂ non-magnetic granular underlayer, CoCrPt-SiO ₂ · TiO ₂ granular magnetic layer, hydrogenated carbon protective film, and perfluoropolyether lubricating layer as the top layer by dipping method to form a magnetic recording medium (Magnetic disk) was obtained. When the magnetic disk thus obtained was incorporated into a hard disk drive and checked for operation, the expected performance was obtained.

DESCRIPTION OF SYMBOLS 1 Glass outflow pipe 2 Molten glass flow 3-1, 3-2 Shear blade 4 Molten glass lump 5, 6 Press molding die 5-1, 5-2 Press molding main body 6-1, 6-2 Guide member

Claims (6)

The molten glass stream flowing out from the glass outlet is cut to separate the molten glass lump, and the molten glass lump is press-molded into a disk or a substantially disk-shaped thin glass using a press mold, and the substrate for a magnetic recording medium In the manufacturing method of the glass blank which produces the glass blank processed into,
In the state where the molten glass flow flowing out from the glass outlet is suspended in the air, the molten glass flow is cut, the molten glass lump is separated and dropped, and the falling molten glass lump is pressed flat. Pressing on the surface to form the thin glass,
And the diameter of the said glass outlet is determined so that ratio B / A of the length B of the vertical direction with respect to the largest diameter A in the horizontal cross section of the said molten glass lump at the time of isolation | separation may be in the range of 0.5-5. The molten glass flow temperature is controlled so that the molten glass flow viscosity is constant in the range of 500 to 1050 dPa · s , and further from the cutting position of the molten glass flow to the center of the press molding surface of the press mold. The manufacturing method of the glass blank characterized by making the height difference of 1000 mm or less . Converted to oxide standards, as a glass component, expressed in mol%,
The SiO ₂ 50~75%,
1 to 15% of Al ₂ O ₃ ,
LiO _2, 12 to 35% in total of at least one component selected from Na ₂ O and _{K 2} O,
0 to 20% in total of at least one component selected from MgO, CaO, SrO, BaO and ZnO, and ZrO ₂ , TiO ₂ , La ₂ O ₃ , Y ₂ O ₃ , Ta ₂ O ₅ , Nb ₂ 0 to 10% in total of at least one component selected from O ₅ and HfO ₂ ;
The method for producing a glass blank according to claim 1, wherein the thin glass plate made of glass is press-molded. In addition to the glass component, the glass blank according to claim 1 or 2, the thin plate glass made of glass doped with Ce oxides 0.1 to 3.5 wt% in the outer split, characterized in that press-molding Manufacturing method. In addition to the glass component, Sn oxide and Ce oxide are added, and the total addition amount of the Sn oxide and Ce oxide is 0.1 to 3.5% by mass, the Sn oxide and Ce The mass ratio of the added amount of Sn oxide to the total added amount of oxide (added amount of Sn oxide / (added amount of Sn oxide + added amount of Ce oxide)) is 0.01 to 0.99. The method for producing a glass blank according to claim 1 or 2 , wherein the glass sheet made of glass is press-molded. A magnetic recording medium substrate is manufactured through at least a polishing step for polishing a main surface of a glass blank produced by the method for producing a glass blank according to any one of claims 1 to 4. A method for manufacturing a medium substrate. A magnetic recording medium is manufactured through at least a magnetic recording layer forming step of forming a magnetic recording layer on the magnetic recording medium substrate manufactured by the method for manufacturing a magnetic recording medium substrate according to claim 5. A method for manufacturing a recording medium.