WO2012043704A1 - 磁気記録媒体ガラス基板用ガラスブランク製造方法、磁気記録媒体ガラス基板製造方法、磁気記録媒体製造方法、および、磁気記録媒体ガラス基板用ガラスブランクの製造装置 - Google Patents
磁気記録媒体ガラス基板用ガラスブランク製造方法、磁気記録媒体ガラス基板製造方法、磁気記録媒体製造方法、および、磁気記録媒体ガラス基板用ガラスブランクの製造装置 Download PDFInfo
- Publication number
- WO2012043704A1 WO2012043704A1 PCT/JP2011/072337 JP2011072337W WO2012043704A1 WO 2012043704 A1 WO2012043704 A1 WO 2012043704A1 JP 2011072337 W JP2011072337 W JP 2011072337W WO 2012043704 A1 WO2012043704 A1 WO 2012043704A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- glass
- press
- magnetic recording
- recording medium
- press mold
- Prior art date
Links
Images
Classifications
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/84—Processes or apparatus specially adapted for manufacturing record carriers
- G11B5/8404—Processes or apparatus specially adapted for manufacturing record carriers manufacturing base layers
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B30—PRESSES
- B30B—PRESSES IN GENERAL
- B30B11/00—Presses specially adapted for forming shaped articles from material in particulate or plastic state, e.g. briquetting presses, tabletting presses
- B30B11/02—Presses specially adapted for forming shaped articles from material in particulate or plastic state, e.g. briquetting presses, tabletting presses using a ram exerting pressure on the material in a moulding space
- B30B11/027—Particular press methods or systems
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B30—PRESSES
- B30B—PRESSES IN GENERAL
- B30B15/00—Details of, or accessories for, presses; Auxiliary measures in connection with pressing
- B30B15/30—Feeding material to presses
- B30B15/302—Feeding material in particulate or plastic state to moulding presses
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B11/00—Pressing molten glass or performed glass reheated to equivalent low viscosity without blowing
- C03B11/06—Construction of plunger or mould
- C03B11/08—Construction of plunger or mould for making solid articles, e.g. lenses
- C03B11/088—Flat discs
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B7/00—Distributors for the molten glass; Means for taking-off charges of molten glass; Producing the gob, e.g. controlling the gob shape, weight or delivery tact
- C03B7/10—Cutting-off or severing the glass flow with the aid of knives or scissors or non-contacting cutting means, e.g. a gas jet; Construction of the blades used
- C03B7/11—Construction of the blades
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B2215/00—Press-moulding glass
- C03B2215/70—Horizontal or inclined press axis
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P40/00—Technologies relating to the processing of minerals
- Y02P40/50—Glass production, e.g. reusing waste heat during processing or shaping
- Y02P40/57—Improving the yield, e-g- reduction of reject rates
Definitions
- the present invention relates to a glass blank manufacturing method for a magnetic recording medium glass substrate, a magnetic recording medium glass substrate manufacturing method, a magnetic recording medium manufacturing method, and a glass blank manufacturing apparatus for a magnetic recording medium glass substrate.
- a method for producing a magnetic recording medium glass substrate typically, (1) a method of producing a molten glass lump through a press molding step of press molding a molten glass lump with a pair of press molds (hereinafter referred to as “ (Refer to Patent Documents 1 to 3), and (2) a method of producing a sheet-like glass formed by a float method, a downdraw method, or the like through a step of cutting into a disk shape ( Hereinafter, it may be referred to as “sheet-like glass cutting method” (see Patent Document 4).
- a lapping process (rough polishing process) and a polishing process (precision polishing process) are performed as polishing processes after a disk processing process for processing sheet glass into a disk shape.
- a polishing process precision polishing process
- the sheet-like glass cutting method disclosed in Patent Document 4 discloses that the lapping process (rough polishing process) is omitted as the polishing process and only the polishing process (precision polishing process) is performed.
- the molten glass lump is usually arranged on the lower mold, and then the vertical direction relative to the molten glass lump by the upper mold and the lower mold.
- the magnetic recording medium is further subjected to a press forming process by press forming a molten glass lump by applying a pressing force (hereinafter also referred to as “vertical direct press”), followed by a lapping process, a polishing process, etc.
- a glass substrate is obtained.
- the lapping process is omitted by using a high-rigidity material as the material of the upper mold, the lower mold, and the parallel spacer arranged between the upper mold and the lower mold. It has also been proposed.
- Patent Document 3 there is a method in which an upper die for cooling is placed on a press-molded product after press molding in order to obtain a plate-like glass having a small warp while preventing a decrease in productivity. Proposed.
- the cooling state of the upper and lower surfaces of the press-molded product is balanced by using an upper die for cooling.
- the press molding process is performed by applying a pressing force from the horizontal direction to the molten glass lump by a pair of press molds arranged to face each other in the horizontal direction. It has also been proposed to carry out the method by an addition method (hereinafter sometimes referred to as “horizontal direct press”).
- JP 2009-149477 A (Claim 1, paragraph number 0012, etc.) Japanese Patent Laid-Open No. 2003-54965 (claims, paragraph numbers 0040 and 0043, FIGS. 4 to 8 etc.) Patent No. 4380379 (paragraph 0031, FIGS. 1 to 9 etc.) Japanese Patent Laid-Open No. 2003-36528 (FIGS. 3 to 6, FIG. 8, etc.)
- the lapping process performed mainly for the purpose of ensuring the flatness and thickness uniformity of the magnetic recording medium glass substrate and adjusting the plate thickness is omitted. Or shortening the time is very effective. This is because the wrapping process requires a wrapping apparatus for implementation, increasing the number of steps for producing a magnetic recording medium glass substrate and increasing the processing time. In addition, the lapping process may cause cracks on the glass surface, and the present situation is that the omission of the lapping process is being studied.
- the sheet-like glass cutting method is compared with the press method, and the sheet-like glass with high flatness produced by the float method, down-draw method, etc. is used.
- the sheet-shaped glass cutting method for processing is more advantageous.
- the press method has an advantage that the glass utilization efficiency is higher than the sheet-like glass cutting method.
- the viscosity of the lower surface of the molten glass block arranged on the lower mold is locally increased.
- the press molding is performed on the molten glass lump in which a large viscosity distribution (temperature distribution) is generated, and thus a portion that is difficult to stretch is generated by pressing.
- the cooling rate after press molding also differs for each part of the glass molded body that has been press-molded and stretched into a plate shape. For this reason, in the glass blank produced using a vertical direct press, plate
- the horizontal direct press exemplified in Patent Document 3
- the horizontal direct press has a uniform viscosity distribution of the molten glass lump at the time of press molding, and therefore it is easy to stretch the molten glass lump thinly and uniformly.
- the horizontal direct press in comparison with the vertical direct press, in principle, it is considered that the horizontal direct press is easier to drastically suppress the increase in the plate thickness deviation and the decrease in flatness of the glass blank.
- the thickness deviation and flatness of glass magnetic recording medium glass substrates and glass blanks used for the production of magnetic recording media should be further improved. Is required.
- the first invention, the second invention, and the third invention share a common problem of improving flatness.
- the first invention and the third invention are made in view of the first situation, and a glass blank for a magnetic recording medium glass substrate capable of producing a glass blank having excellent flatness. It is an object (first problem) to provide a manufacturing method, a magnetic recording medium glass substrate manufacturing method using the manufacturing method, and a magnetic recording medium manufacturing method.
- the second aspect of the present invention has been made in view of the second situation, and even when a glass blank is manufactured by a horizontal direct press, a glass blank having a smaller plate thickness deviation and flatness can be manufactured.
- Manufacturing method of glass blank for magnetic recording medium glass substrate, magnetic recording medium glass substrate manufacturing method using the manufacturing method of glass blank for magnetic recording medium glass substrate, magnetic recording medium manufacturing method, and magnetic recording medium glass substrate An object of the present invention is to provide a glass blank manufacturing apparatus (second problem).
- the first problem including the common problem is achieved by the following first invention. That is, The method for manufacturing a glass blank for a magnetic recording medium glass substrate according to the first aspect of the present invention is the first press molding in which the falling molten glass lump is disposed opposite to the direction intersecting the falling direction of the molten glass lump. A first press step of pressing the mold and the second press mold to form a plate, and a plate glass formed between the first press mold and the second press mold. A second press step that continues pressing with one press mold and a second press mold, and after the second press step, the first press mold and the second press mold are separated from each other.
- a glass blank for a magnetic recording medium glass substrate is manufactured through at least a take-out step of taking out the sheet glass sandwiched between the first press mold and the second press mold, and at least the first The pressing process and the second During the implementation period of the less process, the temperature of the press molding surface of the first press mold and the temperature of the press molding surface of the second press mold are substantially the same. Pressing the molten glass lump after bringing the press molding surface of the first press mold and the press molding surface of the second press mold substantially into contact with the molten glass lump, and second The duration of the pressing step is controlled so that the flatness of the glass blank for a magnetic recording medium glass substrate is 10 ⁇ m or less (within 10 ⁇ m).
- the duration of the second pressing step is set so that the temperature of the plate glass at the end of the second pressing step is at least It is preferable to select the temperature so as to be equal to or lower than the temperature obtained by adding 10 ° C. to the strain point of the glass material constituting the plate glass.
- the molten glass is suspended from the glass outlet and continuously flows downward in the vertical direction. It is preferable to include a molten glass lump forming step of forming a molten glass lump by cutting the tip portion.
- the viscosity of the molten glass is preferably in the range of 500 dPa ⁇ s to 1050 dPa ⁇ s.
- the first press mold and the second press mold are orthogonal to the falling direction of the molten glass lump. It is preferable that they are arranged to face each other.
- Another embodiment of the method for producing a glass blank for a magnetic recording medium glass substrate according to the first aspect of the present invention is the press of the first press mold and the second press mold immediately before the first press step.
- the absolute value of the in-plane temperature difference of the molding surface is preferably in the range of 0 ° C to 100 ° C.
- the pressing pressure in the second pressing step is decreased with time.
- the press pressure is a plate shape sandwiched between the first press mold and the second press mold. It is preferable to reduce the temperature of the glass when it falls within the range of the yield point ⁇ 30 ° C. of the glass material constituting the plate glass.
- Another embodiment of the method for producing a glass blank for a magnetic recording medium glass substrate according to the first aspect of the present invention is the press of one surface of the sheet glass and the first press mold during the second pressing step. It is preferable that the molding surface is always in close contact with no gap, and the other surface of the sheet glass is always in close contact with the press molding surface of the second press mold.
- the flatness of the glass blank for a magnetic recording medium glass substrate is 4 ⁇ m or less (4 ⁇ m). It is preferable to control so that it is within.
- Another embodiment of the method for producing a glass blank for a magnetic recording medium glass substrate according to the first aspect of the present invention is the region in contact with at least the plate-like glass on the press molding surface of the first press mold and the second press mold. However, it is preferable that it is a substantially flat surface.
- a method of manufacturing a magnetic recording medium glass substrate comprising: a first press-molding die in which a falling molten glass lump is disposed opposite to a direction intersecting a dropping direction of the molten glass lump; A first press step of pressing into a plate by pressing with a second press mold, and a plate glass formed between the first press mold and the second press mold with the first press The second press step that continues to be pressed by the mold and the second press mold, and after passing through the second press step, the first press mold and the second press mold are separated, A glass blank for a magnetic recording medium glass substrate is manufactured at least through a take-out step of taking out the glass sheet sandwiched between the first press mold and the second press mold, and then the magnetic recording medium glass substrate Main surface of glass blank for At least through a polishing step for polishing, a magnetic recording medium glass substrate is manufactured, and at least during the execution period of the first press step and the second press step, the temperature of the press forming surface of
- the duration of the second pressing step is set so that the temperature of the glass sheet at the end of the second pressing step is at least a plate It is preferable to select so that it may become below the temperature which added 10 degreeC to the strain point of the glass material which comprises glassy glass.
- the flatness of the glass blank for the magnetic recording medium glass substrate and the flatness of the magnetic recording medium glass substrate are substantially the same. preferable.
- a method for producing a magnetic recording medium comprising: a first press molding die in which a falling molten glass lump is disposed opposite to the direction in which the molten glass lump is dropped;
- the first press molding die is formed by pressing a first pressing step that is pressed by a press molding die into a plate shape, and the plate glass formed between the first press molding die and the second press molding die.
- the second press mold and after the second press process, the first press mold and the second press mold are separated and the first press mold is separated.
- a glass blank for a magnetic recording medium glass substrate is produced at least through a take-out step of taking out the sheet glass sandwiched between the press mold of the second press molding die and the glass for the magnetic recording medium glass substrate Polishing the main surface of the blank
- the magnetic recording medium glass substrate is manufactured through at least the steps, and the magnetic recording medium is formed through at least the magnetic recording layer forming step of forming the magnetic recording layer on the magnetic recording medium glass substrate.
- the temperature of the press molding surface of the first press mold and the temperature of the press molding surface of the second press mold are substantially the same.
- the molten glass lump is pressed after the press molding surface of the first press mold and the press molding surface of the second press mold are brought into contact with the molten glass lump substantially simultaneously.
- the duration of the second pressing step is controlled so that the flatness of the glass blank for a magnetic recording medium glass substrate is 10 ⁇ m or less (within 10 ⁇ m).
- the duration of the second press step is set so that the temperature of the plate glass at the end of the second press step is at least the plate glass. It is preferable to select the temperature to be equal to or lower than the temperature obtained by adding 10 ° C. to the strain point of the glass material constituting the glass.
- the flatness of the glass blank for the magnetic recording medium glass substrate and the flatness of the magnetic recording medium glass substrate are substantially the same.
- the second problem including the common problem is achieved by the following second invention. That is,
- the method for producing a glass blank for a magnetic recording medium glass substrate according to the second aspect of the present invention is the first press molding in which the falling molten glass lump is arranged opposite to the direction intersecting the falling direction of the molten glass lump.
- a glass blank for a magnetic recording medium glass substrate is manufactured at least through a press molding step of press molding using a mold and a second press mold, and at least the first press mold has a press molding surface. And, during press molding, when it is extruded to the side of the second press mold disposed opposite to the press molding surface, it comes into contact with a part of the second press mold disposed opposite to the press molding surface.
- a guide member having at least a function of maintaining a substantially constant distance between the press molding surfaces of the first press mold and the second press mold. Until the first press mold and the second press mold are brought into contact with each other until the first press mold and the second press mold are brought into contact with each other. In a state where the first step of forming the glass sheet, the first press mold guide member, and the second press mold are in contact with each other, the first press mold main body, And a second step of further pressing the sheet glass with the second press mold.
- the first press mold and the second press mold each have a press mold body having a press molding surface.
- the first press mold is brought into contact with a part of the other press mold disposed opposite to the press molding surface when extruded to the other press mold side disposed opposite to the press molding surface.
- the second press mold guide member are brought into close contact with each other until the second press mold is brought into contact with each other, and the second step is performed.
- the press mold body of the first press mold, the press mold body of the second press mold It is preferable to carry out by further pressing the sheet glass.
- Another embodiment of the method for producing a glass blank for a magnetic recording medium glass substrate according to the second aspect of the present invention is a method of dropping a molten glass from a glass outlet and continuously flowing out downward in the vertical direction. It is preferable to include a molten glass lump forming step of forming a molten glass lump by cutting the tip portion.
- the viscosity of the molten glass is preferably in the range of 500 dPa ⁇ s to 1050 dPa ⁇ s.
- the first press mold and the second press mold are orthogonal to the falling direction of the molten glass lump. It is preferable that they are arranged to face each other.
- the flatness of the glass blank for the magnetic recording medium glass substrate is 10 ⁇ m or less (within 10 ⁇ m). It is preferable to control so that.
- the duration of the second step is set so that the temperature of the glass sheet at the end of the second step is at least: It is preferable to select the temperature to be equal to or lower than the temperature obtained by adding 10 ° C. to the strain point of the glass material constituting the plate glass.
- the temperature of the press molding surface of the first press mold immediately before the first step is performed, It is preferable that the absolute value of the difference between the temperature of the press mold of the press mold and the press mold is in the range of 0 ° C. to 10 ° C.
- Another embodiment of the method for producing a glass blank for a magnetic recording medium glass substrate according to the second aspect of the present invention is the press molding of the first press mold and the second press mold immediately before the first step is performed.
- the absolute value of the in-plane temperature difference between the surfaces is preferably in the range of 0 ° C to 100 ° C.
- Another embodiment of the method for producing a glass blank for a magnetic recording medium glass substrate according to the second aspect of the present invention includes the temperature of the press molding surface of the first press mold at least during the press molding step, The temperature of the press molding surface of the press mold is substantially the same, and the press molding surface of the first press mold and the press molding surface of the second press mold are made of molten glass lump. It is preferable to press-mold the molten glass lump after contact with each other substantially simultaneously.
- the temperature of the plate glass is at least 10 ° C. added to the strain point of the glass material constituting the plate glass.
- the second step is preferably continued until:
- the pressing pressure in the second step is decreased with time.
- the press pressure is a plate shape sandwiched between the first press mold and the second press mold. It is preferable to reduce the temperature of the glass when it falls within the range of the yield point ⁇ 30 ° C. of the glass material constituting the plate glass.
- the flatness of the glass blank for a magnetic recording medium glass substrate is preferably 10 ⁇ m or less (within 10 ⁇ m).
- the flatness of the glass blank for a magnetic recording medium glass substrate is preferably 4 ⁇ m or less (within 4 ⁇ m).
- the region of the first press mold and the press molding surface of the second press mold that is in contact with at least the plate glass is a substantially flat surface.
- each of the first press mold and the second press mold includes a press mold body and a guide member.
- a first extruding member that simultaneously extrudes to the other press mold side that is in a direction perpendicular to the press molding surface and is opposed to the press molding surface, and a guide member by the first extrusion member After the part of the other press mold placed opposite to the press molding surface comes into contact, the other side of the press mold body in the direction orthogonal to the press molding surface and opposed to the press molding surface It is preferable to further include a second extruding member that extrudes to the press mold side.
- the method of manufacturing a magnetic recording medium glass substrate according to the second aspect of the present invention includes a first press molding die in which a falling molten glass lump is disposed to face in a direction intersecting with a dropping direction of the molten glass lump.
- the magnetic material is subjected to at least a polishing step for polishing the main surface of the glass blank for a magnetic recording medium glass substrate.
- a recording medium glass substrate is manufactured, and at least a first press mold is extruded to a press mold body having a press mold surface and a second press mold side disposed opposite to the press mold surface during press molding.
- Press forming die body, and press forming when pressed to the second press forming die side arranged opposite to the press forming surface A guide having at least a function of maintaining a substantially constant distance between the press forming surfaces of the first press mold and the second press mold by contacting a part of the second press mold disposed opposite to the first press mold.
- the first press mold and the second press mold until the press molding process makes contact with the guide member of the first press mold and the second press mold.
- the first press with the first step of forming the molten glass lump into a sheet glass by bringing them close to each other, the guide member of the first press mold, and the second press mold And a second step of continuing to press the sheet glass by the press mold main body of the mold and the second press mold.
- the flatness of the glass blank for a magnetic recording medium glass substrate and the flatness of the magnetic recording medium glass substrate are substantially the same.
- the apparatus for producing a glass blank for a magnetic recording medium glass substrate includes a molten glass outlet pipe having an outlet for dropping a molten glass flow downward in the vertical direction, and a molten gas flowing out of the molten glass outlet pipe. It is a direction that is substantially perpendicular to the direction in which the glass flow hangs, and is disposed opposite to both sides of the direction in which the molten glass flow hangs, and cuts the tip of the molten glass flow by penetrating from both sides of the molten glass flow.
- a molten glass lump is directly pressed using a pair of press molds arranged opposite to each other and having substantially the same temperature.
- a method for producing a glass blank for a magnetic recording medium glass substrate including a molding step for molding a sheet glass, wherein the temperature of the molten glass lump is at the strain point of the glass material constituting the sheet glass in the molding step.
- the molten glass lump is continuously pushed with a pair of press molds until the temperature is 10 ° C. or lower.
- One embodiment of the method for producing a glass blank for a magnetic recording medium glass substrate according to the third aspect of the present invention is to add a molten glass mass and a pair of press molds until the temperature of the molten glass mass is equal to or lower than the strain point of the glass material. It is preferable to perform an annealing treatment after maintaining the close contact state.
- the forming step includes a first pressing step for determining the plate thickness of the plate glass, and Including a second press step for improving flatness, and the first press step and the second press step are preferably performed continuously using a pair of press molds.
- the forming step is performed so that the thickness of the plate glass is 2 mm or less and the flatness is 10 ⁇ m or less. It is preferable to implement.
- a glass blank for a magnetic recording medium glass substrate is produced by the method of manufacturing a glass blank for a magnetic recording medium glass substrate of the third present invention.
- a magnetic recording medium glass substrate is produced by processing a glass blank for a substrate.
- a magnetic recording medium glass substrate is produced by the method of manufacturing a magnetic recording medium glass substrate of the third present invention, and a magnetic recording layer is formed on the magnetic recording medium glass substrate.
- a magnetic recording medium is manufactured through at least a magnetic recording layer forming step.
- a method for producing a glass blank for a magnetic recording medium glass substrate capable of producing a glass blank having a smaller thickness deviation and flatness and A magnetic recording medium glass substrate manufacturing method, a magnetic recording medium manufacturing method, and a glass blank manufacturing apparatus for a magnetic recording medium glass substrate using the method for manufacturing a glass blank for a magnetic recording medium glass substrate can be provided.
- the manufacturing method of the glass blank of 1st it is a schematic cross section explaining a part of all the processes. In an example of the manufacturing method of the glass blank of 1st this embodiment, it is a schematic cross section explaining the other part of all the processes. It is a schematic cross section which shows an example of the molten glass lump in the fall. In an example of the manufacturing method of the glass blank of 1st this embodiment, it is a schematic cross section explaining the other part of all the processes. In an example of the manufacturing method of the glass blank of 1st this embodiment, it is a schematic cross section explaining the other part of all the processes. In an example of the manufacturing method of the glass blank of 1st this embodiment, it is a schematic cross section explaining the other part of all the processes.
- the method for producing a glass blank for a magnetic recording medium glass substrate according to the first embodiment refers to dropping a molten glass lump that is falling.
- a first press mold and a second press mold that are pressed by a first press mold and a second press mold that are arranged to face each other in a direction intersecting the direction, and the first press mold and the second press mold After the second press step, the plate glass formed between the first press mold and the second press step continues to be pressed with the first press mold and the second press mold.
- magnetic recording medium glass substrate means a glass substrate for a magnetic recording medium made of amorphous glass (amorphous glass).
- the temperature is sufficiently higher than the strain point of the glass material as in the conventional pressing method, and the molten glass maintains an easily deformable state.
- the lump is pressed and formed into a plate shape.
- the molten glass mass is pressed.
- the temperature of the press molding surface of the first press mold and the temperature of the press molding surface of the second press mold Are substantially identical.
- both sides of the molten glass block being formed into a plate shape in the first press step and the plate glass in a state of being sandwiched between a pair of press molds in the second press step are always symmetrical. It will continue to be cooled.
- the glass blank manufacturing method of the first embodiment is press-molded as compared with the vertical direct press that press-molds a molten glass lump in a state in which a viscosity distribution is generated by contact with the lower mold for a long time. After that, the temperature difference between the both surfaces of the plate-like glass hardly occurs, and the flatness due to the temperature difference between both surfaces can be surely suppressed.
- the glass sheet just after the first pressing step has high temperature and high fluidity (low viscosity). For this reason, it is in the state which flat glass tends to deform
- the glass sheet formed between the first press mold and the second press mold is used as the first press step.
- the duration of the second pressing step is controlled so that the flatness of the glass blank is 10 ⁇ m or less (within 10 ⁇ m).
- the duration of the second pressing step is preferably controlled so that the flatness of the glass blank is 4 ⁇ m or less (within 4 ⁇ m).
- the flatness of the produced glass blank can be made more excellent.
- the duration of a 2nd press process is short, distortion will arise in the plate glass of a cooling process by disturbance, and the said distortion will worsen the flatness of a glass blank. Therefore, the duration of the second press step is changed, the flatness of the obtained glass blank is measured, and as a result, the duration of the second press step is set so that the flatness is 10 ⁇ m or less (within 10 ⁇ m). Set and manufacture a glass blank.
- the duration of the second pressing step may be set in consideration of the flatness and productivity of the glass blank. From these viewpoints, the duration of the second pressing step is specifically preferably in the range of 2 to 40 seconds, and more preferably in the range of 2 to 30 seconds.
- the second pressing step in order to control the flatness of the glass blank to 10 ⁇ m or less (within 10 ⁇ m), in the second pressing step, the fluidity of the sheet glass is lost, and the temperature range is virtually impossible to deform. It is particularly preferable to select the duration of the second pressing step so as to continue pressing the sheet glass. In this case, the glass sheet can be solidified while maintaining a state in which the deformation of the glass sheet immediately after the first pressing step is suppressed. Therefore, the flatness of the produced glass blank can be made more excellent.
- the duration in the second pressing step is equal to or lower than the temperature at which the temperature of the plate glass at the end of the second pressing step is 10 ° C. added to the strain point of the glass material constituting the plate glass.
- the temperature is equal to or lower than the temperature obtained by adding 5 ° C. to the strain point, and further preferable to select so as to be equal to or lower than the strain point.
- the lower limit temperature of the temperature of the sheet glass at the end of the second pressing step is not particularly limited, but it is practical from the viewpoint of suppressing the productivity reduction due to the increase in time required for the second pressing step.
- the strain point is preferably higher than the strain point. Therefore, it is preferable that the upper limit value of the duration time in the second pressing step is also selected from this viewpoint.
- the temperature of the press molding surface of the first press mold and the second press at least during the first press step and the second press step. It is necessary that the temperature of the press molding surface of the mold is substantially the same.
- substantially the same means that the absolute value of the temperature difference between the temperature of the press molding surface of the first press mold and the temperature of the press molding surface of the second press mold is within 10 ° C. It means that there is.
- the absolute value of this temperature difference is more preferably within 5 ° C, most preferably 0 ° C.
- the “temperature of the press molding surface” means a temperature near the center of the press molding surface.
- the absolute value of the temperature difference between the upper mold press surface and the lower mold press surface during the press molding of the molten glass lump is also determined by the press molding conditions. However, it is generally about 50 ° C to 100 ° C.
- the molten glass lump is brought into contact with the molten glass lump substantially simultaneously with the press molded surface of the first press mold and the press molded surface of the second press mold. Press.
- substantially simultaneously contact means that the absolute value of the time difference between the time when the molten glass block and one press-molded surface are in contact with the point when the molten glass block and the other press-formed surface are in contact with each other. It means within 0.1 seconds. The absolute value of this time difference is more preferably within 0.05 seconds, and most preferably 0 seconds.
- the time required for the molten glass lump to contact the upper press forming surface after the molten glass lump contacts the upper press forming surface depends on the press forming conditions. Although it depends, it is generally about 1.5 to 3 seconds.
- the first press mold is as early as possible even when mass-producing glass blanks by horizontal direct press, which is the same press method as the vertical direct press in that press molding is performed by a pair of press molds. It is considered that it is extremely important to separate the glass plate from the second press mold and take out the sheet glass. Thereby, after the molten glass lump has been formed into a sheet glass, it is easy to achieve both the productivity and the improvement of the flatness of the glass blank. Therefore, when mass-producing glass blanks by horizontal direct pressing, after the molten glass lump becomes plate-like glass, the plate-like glass is heated until the temperature becomes equal to or lower than the temperature obtained by adding 10 ° C. to the strain point.
- the molten glass lump is placed in the lower mold and then press molding is performed. For this reason, a molten glass lump in which a large temperature distribution (viscosity distribution) has been brought into contact with the lower mold for a long time must be press-formed by the upper mold and the lower mold.
- the molten glass lump that is falling is press-molded so as to be sandwiched between a pair of press-molding dies. That is, since the molten glass lump does not continue to contact one of the press molds until the press molding is started, as a result, the temperature distribution (viscosity distribution) of the molten glass lump at the start of press molding is Extremely uniform.
- the cooling rate of the molten glass lump and the sheet glass is determined by the temperature of the pair of press molds in contact with the molten glass lump, assuming that the heat capacity of the press mold is the same regardless of the press method. The That is, at the start of press molding, the cooling rate increases if a low-temperature press mold is used, and the cooling rate decreases if a high-temperature press mold is used.
- the vertical direct press since the lower mold and the molten glass lump are in contact for a long time before the press molding is started, the lower mold is melted until the press molding is started. It will be heated by the glass lump.
- press molding is always started in a state where one of the press molds (lower mold) is at a high temperature.
- This fact means that it is much easier to increase the cooling rate of the molten glass lump and the sheet glass in the horizontal direct press than in the vertical direct press.
- the time required to cool the molten glass lump into a plate shape and then cool down to the vicinity of the strain point is much greater with the horizontal direct press than with the vertical direct press. Obviously, it can be shortened. Therefore, even if the second pressing step is performed in the horizontal direct press, the productivity is not lowered so much as to impair the practicality that occurs in the vertical direct press.
- the manufacturing method of the glass blank of 1st this embodiment demonstrated above is not specifically limited if it includes at least a 1st press process, a 2nd press process, and an extraction process, Usually, a molten glass lump It is preferable to have a forming step. Below, each process including a molten glass lump formation process is demonstrated in detail. In the following description, description of points already described above is omitted.
- a molten glass lump that is an object of press molding is produced.
- a method for producing a molten glass lump usually, by dropping the molten glass from the glass outlet and cutting the tip of the molten glass flow that continuously flows out downward in the vertical direction, A molten glass lump is formed.
- a pair of shear blades can be used for cutting performed so as to separate the tip from the molten glass stream.
- the viscosity of the molten glass is not particularly limited as long as it is suitable for cutting of the tip portion or press molding, but is usually controlled to a constant value within a range of 500 dPa ⁇ s to 1050 dPa ⁇ s. It is preferable.
- a molten glass flow 20 is provided from a glass outlet 12 provided at the lower end of a molten glass outlet pipe 10 whose upper end is connected to a molten glass supply source (not shown). Is continuously discharged downward in the vertical direction.
- the first shear blade (lower blade) 30 and the second shear blade (upper blade) 40 are melted on both sides of the molten glass flow 20, respectively. It arrange
- the lower blade 30 and the upper blade 40 are each orthogonal to the central axis D, and in the drawing, are orthogonal to the direction of the arrow X1 that proceeds from the left side to the right side, and the central axis D. And it moves to the front-end
- the viscosity of the molten glass flow 20 is controlled by adjusting the temperature of the molten glass outflow pipe 10 or the molten glass supply source upstream thereof.
- the lower blade 30 and the upper blade 40 are provided on the substantially plate-like main body portions 32 and 42 and the end portions of the main body portions 32 and 42, and a molten glass flow that continuously flows downward in the vertical direction. It has the blade parts 34 and 44 which cut
- the upper surface 34U of the blade portion 34 and the lower surface 44B of the blade portion 44 form a surface that substantially coincides with the horizontal plane, and the lower surface 34B of the blade portion 34 and the upper surface 44U of the blade portion 44 intersect with the horizontal plane.
- An inclined surface is formed.
- the lower blade 30 and the upper blade 40 are arranged so that the upper surface 34U of the blade part 34 and the lower surface 44B of the blade part 44 are at substantially the same height with respect to the vertical direction.
- the upper blade 34U and the lower surface 44B of the blade portion 44 are moved further by moving the lower blade 30 and the upper blade 40 in the directions of the arrow X1 and the arrow X2, respectively.
- the lower blade 30 and the upper blade 40 penetrate into the molten glass flow 20 to the vicinity of the central axis D, and the tip 22 is cut as a substantially spherical molten glass lump 24.
- FIG. 2 shows a state in which the front end portion 22 is separated from the main body portion of the molten glass flow 20 as a molten glass lump 24. And as shown in FIG. 3, the molten glass lump 24 cut
- the first press molding die and the second press molding in which the molten glass lump 24 shown in FIG. 3 is arranged to face each other in the direction intersecting the dropping direction of the molten glass lump 24. Press with a mold and mold into a plate.
- the first press mold and the second press mold are opposed to each other in a direction substantially perpendicular to the falling direction of the molten glass lump 24 so as to form an angle within a range of 90 degrees ⁇ 1 degree. It is preferable that they are arranged opposite to each other in a direction perpendicular to the direction in which the molten glass lump 24 falls.
- the pair of press molds so as to face the falling direction of the molten glass lump 24, it is easier to press the molten glass lump 24 from both sides and form it into a plate shape.
- the temperature of the press molding surfaces of the first press mold and the second press mold immediately before the first press step is 10 ° C. at the strain point of the glass material constituting the molten glass lump 24.
- the temperature is preferably equal to or lower than the added temperature, and more preferably equal to or lower than the temperature obtained by adding 5 ° C. to the strain point of the glass material constituting the molten glass lump 24.
- the lower limit value of the temperature of the press molding surfaces of the first press mold and the second press mold immediately before the first press step is not particularly limited, but is due to the rapid cooling of the molten glass lump 24. From the practical point of view, such as preventing cracking of the glass blank and preventing a significant decrease in stretchability of the molten glass lump 24 due to a sudden increase in viscosity during press molding, it is above the strain point of the glass material constituting the molten glass lump 24. Preferably there is.
- the absolute value of the difference between the temperature of the press molding surface of the first press mold and the temperature of the press molding surface of the second press mold immediately before the first pressing step is 0 ° C. to It is preferably within a range of 10 ° C., more preferably within a range of 0 ° C. to 5 ° C., and particularly preferably 0 ° C. In this case, it can suppress more reliably that the temperature difference in both surfaces of the plate glass formed in plate shape by the press of the molten glass lump 24 arises, and, as a result, flatness can be improved more.
- the absolute value of the in-plane temperature difference between the press forming surfaces of the first press mold and the second press mold immediately before the first press step is in the range of 0 ° C. to 100 ° C.
- the temperature is preferably in the range of 0 ° C. to 50 ° C., more preferably 0 ° C.
- the molten glass lump 24 shown in FIG. 3 includes a first press mold 50 and a second press that are opposed to each other in a direction orthogonal to the falling direction Y ⁇ b> 1 of the molten glass lump 24. It enters between the molds 60.
- the first press molding die 50 and the second press molding die 60 before the press molding are arranged symmetrically with respect to the dropping direction Y1 and spaced apart from each other in the orthogonal direction. ing.
- the molten glass lump 24 is press-molded by pressing the molten glass lump 24 from both sides at the timing when the molten glass lump 24 reaches the vicinity of the central portion in the vertical direction of the first press mold 50 and the second press mold 60.
- the first press mold 50 is moved in the direction of the arrow X1 perpendicular to the drop direction Y1 and proceeds from the left side to the right side in the figure, and the second press mold 60 is dropped. It moves in the direction of the arrow X2 that is orthogonal to the direction Y1 and proceeds from the right side to the left side in the figure.
- the moving speed of the first press mold 50 in the arrow X1 direction and the moving speed of the second press mold 60 in the arrow X2 direction are set to be the same or substantially the same.
- the press molds 50 and 60 include press mold main bodies 52 and 62 having a substantially disk shape, and guide members 54 and 64 arranged so as to surround the outer peripheral ends of the press mold main bodies 52 and 62.
- the guide members 54 and 64 are drawn so as to be positioned on both upper and lower sides of the press mold main bodies 52 and 62 in FIG.
- the description of the drive member that moves the press mold 50 in the direction of the arrow X1 and moves the press mold 60 in the direction of the arrow X2 is omitted in the drawing.
- One side of the press mold body 52, 62 is a press mold surface 52A, 62A.
- the first press mold 50 and the second press mold 60 are arranged to face each other so that the press molding surfaces 52 ⁇ / b> A and 62 ⁇ / b> A face each other.
- the guide member 54 is provided with a guide surface 54A at a height position slightly protruding in the X1 direction with respect to the press molding surface 52A, and the guide member 64 is slightly in the X2 direction with respect to the press molding surface 62A.
- 64 A of guide surfaces are provided in the height position which protruded only.
- this gap thickness is the thickness of the molten glass lump 24 that is press-molded between the first press mold 50 and the second press mold 60, that is, the thickness of the glass blank.
- the press molding surfaces 52A and 62A are formed so that the molten glass lump 24 is formed into the press molding surface 52A of the first press molding die 50 and the press molding surface 62A of the second press molding die 60 by performing the first pressing step.
- the entire surface of the press molding surface 52A including the molten glass stretching region S1 and the press molding surface 62A including the molten glass stretching region S2 is a flat surface having a normal and substantially zero curvature.
- the flat surface has only minute unevenness formed by performing normal flattening processing or mirror polishing processing when manufacturing a press mold, and is larger than these minute unevenness. There are no protrusions and / or recesses.
- the glass blank is produced by pressing the molten glass lump 24 by pressing it with the press molding surfaces 52A and 62A. For this reason, the surface roughness of the press molding surfaces 52A and 62A and the surface roughness of the main surface of the glass blank are substantially equal.
- the surface roughness (centerline average roughness Ra) of the main surface of the glass blank is 0.01 to 10 ⁇ m when performing scribing performed as a post-process described later and grinding using a diamond sheet. Since it is desirable to set the range, the surface roughness (centerline average roughness Ra) of the press-molded surface is also preferably in the range of 0.01 to 10 ⁇ m.
- the molten glass lump 24 shown in FIG. 4 falls further downward and enters between the two press molding surfaces 52A and 62A. Then, as shown in FIG. 5, when the press molding surfaces 52 ⁇ / b> A and 62 ⁇ / b> A that are parallel to the drop direction Y ⁇ b> 1 reach the vicinity of the substantially central portion in the up and down direction, 62A is contacted simultaneously or substantially simultaneously.
- the drop distance is determined in consideration of the point that it becomes difficult to press-mold due to the increase in viscosity of the molten glass lump 24 during dropping, or the drop speed becomes too high to cause fluctuations in the press position.
- it is selected within the range of 1000 mm or less, more preferably selected within the range of 500 mm or less, further preferably selected within the range of 300 mm or less, and most preferably selected within the range of 200 mm or less.
- the lower limit of the drop distance is not particularly limited, but is preferably 100 mm or more for practical use.
- the “fall distance” is the moment when the tip 22 is separated as the molten glass lump 24 as illustrated in FIG.
- the position of the press molding start time (the moment of start of press molding), that is, the distance to the vicinity of the substantially central portion in the diametrical direction of the press molding surfaces 52A and 62A parallel to the drop direction Y1. means.
- the plate-like glass 26 shown in FIG. 7 has substantially the same shape and thickness as the finally obtained glass blank. And the size and shape of both surfaces of the sheet glass 26 correspond with the size and shape of molten glass extending
- the time required for the guide surface 54A and the guide surface 64A shown in FIG. 7 to come into contact with each other from the state at the start of press molding shown in FIG. 5 (hereinafter, referred to as “press molding time” in some cases). .) Is preferably within 0.1 seconds from the viewpoint of thinning the molten glass lump 24.
- the guide surface 54A and the guide surface 64A are in contact with each other, so that it is easy to maintain the parallel state between the press molding surface 52A and the press molding surface 62A.
- the minimum of press molding time is not specifically limited, It is preferable that it is 0.05 second or more practically.
- the press mold 50 shown in FIGS. 4 to 7 includes a press mold body 52 and a guide member 54, and the press mold 60 also has the same structure.
- the pair of press molds used in the glass blank manufacturing method of the first embodiment is of the type shown in FIGS. 4 to 7 as long as the molten glass lump 24 can be press molded into a plate shape. It is not limited to things.
- 4 to 7 may be an integrated type in which the press mold main bodies 52 and 62 and the guide members 54 and 64 are integrally formed. It may be a separate type configured as a member.
- the press molds 50 and 60 are separate mold types, in the first pressing step, the press mold body 52 and the guide member 54 move simultaneously and integrally in the direction of the arrow X1, and the press mold body 62 and the guide member 64 move simultaneously and integrally in the direction of the arrow X2.
- the press molding surface 52A and the press molding surface 62A are in a state where the guide member 54 and the guide member 64 are in contact with each other as shown in FIG. Are kept parallel. Therefore, as shown in FIGS. 4 to 6, in the process in which the press mold 50 moves in the direction of the arrow X1 and the press mold 60 moves in the direction of the arrow X2, the press mold surface 52A and the press mold surface 62A Even if the parallel state cannot be maintained, it is easy to make the thickness deviation of the obtained glass blank very small. Therefore, in the drive device for driving the press molds 50 and 60, the press molding surface 52A and the press molding surface 62A are always maintained in an accurate parallel state in the series of processes shown in FIGS. Control ability to control is not required.
- the sheet glass 26 formed between the first press mold 50 and the second press mold 60 is used as the first press mold 50 and the second press mold 60.
- the duration of the second pressing step is controlled so that the flatness of the glass blank is 10 ⁇ m or less (within 10 ⁇ m).
- the temperature of the glass (molten glass lump 24 and plate glass 26) positioned between 62A and 62A is generally about 1200 ⁇ 50 ° C. to 480 ° C. ⁇ 20 ° C., although it depends on the glass material used for press molding. To a large extent.
- the pressing of the sheet glass 26 is continued, so that the fluidity of the sheet glass 26 also decreases with the passage of time.
- the second pressing step there is a difference in the degree of thermal expansion / contraction between both members between the both surfaces of the sheet glass 26 and the press molding surfaces 52A, 62A.
- the force to extend the radial direction of the sheet glass 26 by the press molding surfaces 52A, 62A on both surfaces of the sheet glass 26 which is being thermally contracted that is, A force in the opposite direction to the heat shrinkage acts.
- the fluidity of the sheet glass 26 is greatly reduced as the second pressing process proceeds. Therefore, if excessive stress acts on the sheet glass 26, the plate glass 26 is brittlely fractured. Is likely to occur. For this reason, if a force in the direction opposite to the thermal shrinkage always acts on both surfaces of the plate glass 26, excessive stress acts in the plane direction of the plate glass 26 and the plate glass 26 is broken. Become.
- the press pressure decreases with time means not only when the press pressure decreases with the lapse of time in the second pressing process, but also with the press pressure temporarily with the lapse of time.
- the press pressure may be decreased stepwise with the passage of time, or may be continuously decreased with the passage of time.
- the temperature of the sheet glass 26 sandwiched between the first press mold 50 and the second press mold 60 is reduced. It is preferable that the glass material constituting the plate-like glass 26 is reduced when it falls within the range of the yield point ⁇ 30 ° C. Thereby, the crack of the sheet glass 26 can be more effectively suppressed by a relatively simple operation of the pressing pressure.
- the pressing pressure is assumed to be 1% to 10% after reduction, assuming that 100% before reduction. It is preferable to be in the range of about%.
- the pressing pressure may be changed into a wave shape with time.
- the press pressure can be periodically changed over time, such as a rectangular wave shape or a sine wave shape.
- the coefficient of friction between the both surfaces of the sheet glass 26 and the press-molded surfaces 52A and 62A decreases when the press pressure is near the minimum value over time.
- slip occurs between the both surfaces of the sheet glass 26 and the press molding surfaces 52A and 62A, and a force in the opposite direction to the heat shrinkage that causes cracking acts on both surfaces of the sheet glass 26. It becomes easy to block.
- the plate-like glass 26 undergoes heat shrinkage not only in the diameter direction but also in the thickness direction. For this reason, a slight gap may be generated between the press-molding surface 52A, the press-molding surface 62A, and the sheet glass 26 during the second pressing step.
- the heat conduction efficiency between the two members is lowered.
- a temperature distribution is likely to occur on both sides or in the plane of the sheet glass 26.
- Such a temperature distribution causes a viscosity distribution (fluidity unevenness) in the plate-like glass 26, so that the plate-like glass 26 is likely to be warped and deteriorates the flatness of the obtained glass blank. It becomes easy.
- the one surface of the sheet glass 26 and the press molding surface 52A of the first press mold 50 are always closely adhered without any gaps. It is preferable that the other surface of the plate glass 26 and the press molding surface 62A of the second press mold 60 are always closely adhered without any gap.
- press molds excellent in followability of the press molding surface against thermal shrinkage in the thickness direction of the sheet glass 26 can be used.
- a guide member-less press mold composed of press mold bodies 52, 62 obtained by removing the guide members 54, 64 from the press molds 50, 60, Separate type press molding dies 50 and 60 in which the press mold main bodies 52 and 62 and the guide members 54 and 64 are configured as separate members can be used.
- the second pressing step only the press mold body 52 is pressed in the arrow X1 direction, and only the press mold body 62 is pressed in the arrow X2 direction. Thus, a pressing pressure is applied to the sheet glass 26.
- the first press mold 50 and the second press mold 60 are separated from each other and between the first press mold 50 and the second press mold 60.
- An extraction step of taking out the sandwiched sheet glass 26 is performed. This extraction step can be performed, for example, as described below.
- the first press mold 50 is moved in the arrow X2 direction so as to separate the first press mold 50 and the second press mold 60 from each other.
- the press mold 60 is moved in the arrow X1 direction. Thereby, the press-molding surface 62A and the sheet glass 26 are released.
- FIG. 8 the first press mold 50 is moved in the arrow X2 direction so as to separate the first press mold 50 and the second press mold 60 from each other.
- the press mold 60 is moved in the arrow X1 direction. Thereby, the press-molding surface 62A and the sheet glass 26 are released.
- the press molding surface 52 ⁇ / b> A and the plate glass 26 are released from the mold, and the plate glass 26 is dropped to the lower side Y ⁇ b> 1 in the vertical direction and taken out.
- the press molding surface 52A and the plate-like glass 26 it is possible to release the plate-like glass 26 by applying a force from the outer peripheral direction of the plate-like glass 26. In this case, the sheet glass 26 can be taken out without applying a large force.
- the press molding surface 52A and the plate glass 26 may be released, and then the press molding surface 62A and the plate glass 26 may be released.
- the extracted plate-like glass 26 is annealed as necessary to reduce and remove the distortion, thereby obtaining a base material for processing the magnetic recording medium glass substrate, that is, a glass blank.
- the glass blank obtained by the glass blank manufacturing method of the first embodiment described above can have a flatness of 10 ⁇ m or less (within 10 ⁇ m), or 4 ⁇ m or less (within 4 ⁇ m). Very easy.
- the flatness is preferably 4 ⁇ m or less (within 4 ⁇ m) from the viewpoint of omitting or shortening post-processes performed mainly for improving flatness such as a lapping process.
- the manufacturing method of the glass blank of 1st this embodiment is suitable for manufacture of a glass blank with thinner plate thickness and good flatness. Specifically, it is suitable for manufacturing a glass blank having a plate thickness of 2 mm or less and a flatness of 10 ⁇ m or less (within 10 ⁇ m). A more preferable plate thickness is 1.5 mm or less, a further preferable plate thickness is 1.2 mm or less, and a still more preferable plate thickness is 1.0 mm or less.
- the material constituting the press molds 50 and 60 is preferably a metal or an alloy in consideration of heat resistance, workability, and durability.
- the heat resistance temperature of the metal or alloy constituting the press molds 50 and 60 is preferably 1000 ° C. or higher, and more preferably 1100 ° C. or higher.
- the material constituting the press molds 50 and 60 is preferably spheroidal graphite cast iron (FCD), alloy tool steel (such as SKD61), high speed steel (SKH), cemented carbide, colmonoy, stellite, and the like.
- the press molds 50 and 60 may be cooled using a cooling medium such as water or air to suppress an increase in the temperature of the press molds 50 and 60. Further, in order to make the temperature distribution in the press molding surfaces 52A, 62A uniform, the vicinity of the center of the press molding surfaces 52A, 62A is cooled using a cooling medium, and / or the press mold 50 is used. Further, a heating member such as a heater may be disposed on the outer peripheral side of 60 to heat the outer edge side of the press molding surfaces 52A and 62A.
- a cooling medium such as water or air
- region (molten glass extending
- the surface may have a surface on which a large uneven portion such as a convex portion for forming a V-shaped groove having a depth of about 1/3 to 1/4 of the plate thickness is formed. A surface is preferred.
- the entire pressing surfaces 52A and 62A may be substantially flat surfaces. This is because when a large V-shaped groove is formed in the glass blank, crack defects presumed to be caused by stress concentration in the V-shaped groove portion are likely to occur.
- the “substantially flat surface” means a surface having a very small curvature such as a slight convex surface or a concave surface in addition to a normal flat surface having substantially zero curvature.
- the “substantially flat surface” has minute irregularities formed by performing a normal flattening process or a mirror polishing process when manufacturing a press mold.
- larger protrusions and / or recesses may be provided as necessary as compared with the minute unevenness.
- the convex portion larger than the minute irregularities is substantially point-like having a height of 20 ⁇ m or less with a small possibility of causing deterioration of flow resistance or promoting partial cooling of the molten glass lump. And / or a substantially linear protrusion is acceptable.
- the height is preferably 10 ⁇ m or less, and more preferably 5 ⁇ m or less.
- the convex portion larger than the minute unevenness is not substantially punctiform and substantially linear, and the convex shape is a trapezoidal shape with a minimum width of the top surface of several millimeters or more, or
- the height is allowed to be 50 ⁇ m or less.
- the height is preferably 30 ⁇ m or less, and more preferably 10 ⁇ m or less.
- the side surface of the trapezoidal convex portion has an inclination angle of 0.5 with respect to the top surface. It is preferable to form a plane that forms an angle of less than or equal to a degree, or a curved surface with this plane as a concave surface. The angle is more preferably 0.1 degrees or less.
- the larger concave portion compared with the minute concave and convex portions has a substantially point-like shape having a depth of 20 ⁇ m or less so as not to cause deterioration of the fluidity of the molten glass flowing into the concave portion during press molding. Or if it is a substantially linear recessed part, it will be accept
- the depth is preferably 10 ⁇ m or less, and more preferably 5 ⁇ m or less.
- the concave portion larger than the minute unevenness is not substantially punctiform or substantially linear, and the concave portion having an inverted trapezoidal shape with a minimum width of the top surface of several millimeters or more, or
- the depth is 50 ⁇ m or less. If that is acceptable.
- the depth is preferably 30 ⁇ m or less, and more preferably 10 ⁇ m or less.
- the inclination angle of the side surface of the trapezoidal convex portion is 0.5 degrees with respect to the bottom surface. It is preferable to form a plane having the following angle, or a curved surface with this plane as a concave surface. The angle is more preferably 0.1 degrees or less.
- a press mold (1) a guide member-less press mold, (2) press mold main bodies 52 and 62 and a guide member. 54, 64 are integrally formed press-molding dies 50, 60, and (3) a separate-type press-molding die 52, 62 and guide members 54, 64 are configured as separate members. Press molds 50 and 60 can be used. Among these three types of press molds, it is most preferable to use the separate type press molds 50 and 60 from the viewpoint of achieving the highest balance between higher flatness and smaller thickness deviation. .
- the separation-type press molds 50 and 60 are specifically those having the following structure. That is, as the separation type press mold 50 (or press mold 60), a press mold body 52 having a press mold surface 52A substantially orthogonal to the horizontal direction, and the press mold surface 52A are arranged opposite to each other during press molding. When pressed to the other press mold 60 side, the distance between the press mold surfaces 52A and 62A of the pair of press molds 50 and 60 is reduced by contacting a part of the other press mold 60.
- the guide member 54 having at least a function of keeping constant, the press mold main body 52 and the guide member 54 are simultaneously extruded in the direction substantially orthogonal to the press molding surface 52A and to the other press mold 60 side.
- the press mold main body 52 is A direction scan molding surface 52A substantially perpendicular, and preferably comprises a second pushing member for pushing the other of the pressing mold 60 side, at least.
- FIG. 10 is a schematic cross-sectional view showing an example of a press mold used in the method for manufacturing a glass blank for a magnetic recording medium glass substrate according to the first embodiment.
- 60 is a diagram showing an example.
- the press mold 50S shown in FIG. 10 corresponds to the press mold 50, but the press mold 60 can adopt the same structure.
- the main part of the press mold 50S is composed of a press mold body 52, a guide member 54, a first push member 56, and a second push member 58.
- the central axes of the respective members coincide with each other, and the central axes substantially coincide with the horizontal direction.
- the press-molding die main body 52 is composed of a cylindrical body having one end surface constituting a circular press-molding surface 52A.
- the shape of the press-molding die main body 52 is a columnar shape in the example illustrated in FIG. 10, the shape is not particularly limited as long as it is a substantially columnar shape.
- the press-molding surface 52A is a substantially flat surface.
- the guide member 54 has a length in the axial direction X that is longer than the length in the axial direction X of the press-molding die main body 52 made of a cylindrical body, and accommodates the press-molding die main body 52 on the inner peripheral side.
- one end face (guide face 54A) is formed of a cylindrical body that comes into contact with a guide member (not shown in the drawing) constituting the other press mold.
- the difference between the length of the guide member 54 and the length of the press mold body 52 in the axial direction X in other words, the height difference H between the guide surface 54A and the press molding surface 52A in the axial direction X is the glass produced. This corresponds to approximately half the blank thickness.
- the shape of the guide member 54 is cylindrical, but the shape is not particularly limited as long as it is cylindrical.
- the first extruding member 56 is composed of a disk-shaped member.
- one surface (extruded surface 56A) of the disc-shaped first extruding member 56 is the other end surface (extruded surface 52B) of the press mold main body 52 and the other end surface (extruded surface) of the guide member 54. It consists of a flat surface in contact with the surface 54B).
- a through hole 56 ⁇ / b> H that penetrates in the thickness direction of the first extrusion member 56 is provided in a part of a region facing the extruded surface 52 ⁇ / b> B of the press mold main body 52.
- the surface 56B opposite to the extrusion surface 56A is connected to a first drive device (not shown).
- the first driving device simultaneously pushes the press mold body 52 and the guide member 54 through the first pusher member 56 in the axial direction X in the drawing. It can be extruded from the side where the member 56 is disposed to the side where the press mold main body 52 and the guide member 54 are disposed.
- the shape of the first push member 56 is a disc shape, but the shape is not particularly limited as long as it is a substantially plate shape.
- the through hole 56 ⁇ / b> H is provided as a hole having a circular opening along the center axis X of the press mold main body 52 and the first extrusion member 56. If it is a part of the area
- the second extruding member 58 is composed of a rod-shaped member that is disposed in the through hole 56H and connected to the extruded surface 52B side of the press mold main body 52.
- the second pushing member 58 has a cylindrical bar shape, but the shape is not particularly limited as long as the press mold main body 52 can be moved in the X-axis direction.
- the end opposite to the one end connected to the extruded surface 52B side of the second pushing member 58 is connected to a second drive device (not shown). For this reason, at the time of press molding, only the press mold main body 52 is pressed from the side where the second extruding member 58 is arranged by the second driving device via the second extruding member 58. It can extrude along the X-axis direction to the side where 52 is arranged.
- a glass material used in the method for producing a glass blank of the first embodiment it has physical properties suitable as a magnetic recording medium glass substrate, in particular, a high thermal expansion coefficient, further high rigidity, heat resistance, etc., and There is no particular limitation as long as it can be easily formed into a plate shape by horizontal direct pressing.
- the thermal expansion coefficient is desirably close to the thermal expansion coefficient of the holder that holds the magnetic recording medium.
- the average linear expansion coefficient at 100 to 300 ° C. is preferably 70 ⁇ 10 ⁇ 7 / ° C. or more, more preferably 75 ⁇ 10 ⁇ 7 / ° C. or more, and 80 ⁇ 10 ⁇ 7 / ° C.
- the temperature is not lower than ° C., and it is still more preferable that the temperature is 85 ⁇ 10 ⁇ 7 / ° C. or higher.
- the upper limit value of the average linear expansion coefficient is not particularly limited, but is practically preferably 120 ⁇ 10 ⁇ 7 / ° C. or less.
- a glass material having high rigidity is desired from the viewpoint of reducing the deflection generated during high-speed rotation of the magnetic recording medium.
- the Young's modulus is preferably 70 GPa or more, more preferably 75 GPa or more, and 80 GPa. More preferably, it is more preferably 85 GPa or more.
- the upper limit of the Young's modulus is not particularly limited, but is practically preferably 120 GPa or less.
- the glass transition temperature of the glass material is preferably 600 ° C. or higher, and 610 ° C. The above is more preferable, 620 ° C. or higher is further preferable, and 630 ° C. or higher is more preferable.
- the upper limit of the glass transition temperature is not particularly limited, but is preferably 780 ° C. or lower from a practical viewpoint such as suppressing the temperature during press molding from becoming high. Use of a glass material having a high thermal expansion coefficient, high rigidity, and heat resistance is effective in obtaining a glass substrate suitable for a magnetic recording medium having a high recording density.
- the composition of the glass material a composition that can easily realize physical properties suitable as a magnetic recording medium glass substrate can be appropriately selected.
- the glass composition of a conventional glass material for vertical direct press can be appropriately selected, but an aluminosilicate glass Is preferably selected.
- an aluminosilicate glass since it is easy to make heat resistance, high rigidity, and a high thermal expansion coefficient compatible with balance, especially the composition shown below is especially preferable.
- the glass composition of this glass (hereinafter referred to as “glass composition 1”) is: In mol% display, 50 to 75% of SiO 2 Al 2 O 3 0-5%, Li 2 O 0-3%, ZnO 0-5%, 3 to 15% in total of at least one component selected from Na 2 O and K 2 O; A total of 14 to 35% of at least one component selected from MgO, CaO, SrO and BaO, and 2 to 9% in total of at least one component selected from ZrO 2 , TiO 2 , La 2 O 3 , Y 2 O 3 , Yb 2 O 3 , Ta 2 O 5 , Nb 2 O 5 and HfO 2 ; Including The molar ratio ⁇ (MgO + CaO) / (MgO + CaO + SrO + BaO) ⁇ is in the range of 0.8 to 1, and the molar ratio ⁇ Al 2 O 3 / (MgO + CaO) ⁇ is in the range of 0 to 0.30.
- a preferable range of the average linear expansion coefficient at 100 to 300 ° C. of glass composition 1 is 70 ⁇ 10 ⁇ 7 / ° C. or more, a preferable range of glass transition temperature is 630 ° C. or more, and a preferable range of Young's modulus is 80 GPa or more.
- Glass composition 1 is suitable as a material for an energy-assisted magnetic recording medium glass substrate using a high Ku magnetic material.
- the glass composition 2 As a glass material having a high thermal expansion coefficient, excellent acid resistance and alkali resistance, little alkali elution from the substrate surface, and suitable for chemical strengthening, it has the following glass composition (hereinafter referred to as “glass composition 2”). Things can be shown. That is, the glass composition 2 is In mol% display, SiO 2 and Al 2 O 3 in total 70 to 85%, provided that the content of SiO 2 is 50% or more, the content of Al 2 O 3 is 3% or more, Li 2 O, Na 2 O and K 2 O in total 10% or more, 1 to 6% in total of MgO and CaO, provided that the content of CaO is greater than the content of MgO.
- the manufacturing method of the magnetic recording medium glass substrate of the first embodiment is a magnetic recording medium through at least a polishing step for polishing the main surface of the glass blank produced by the manufacturing method of the glass blank of the first embodiment.
- a glass substrate is manufactured. Specific examples of the respective steps when processing a glass blank to form a magnetic recording medium glass substrate will be described in more detail below.
- Scribe is a glass blank that is cut into two concentric circles (inner concentric circle and outer concentric circle) by a scriber made of super steel alloy or diamond particles 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 difference in the thermal expansion of the glass removes the outer portion of the outer concentric circle and the inner portion of the inner concentric circle. As a result, a perfect circular disk-shaped glass is obtained.
- the outer diameter is substantially the same as the outer diameter of the final magnetic recording medium glass substrate (magnetic disk glass substrate) (when the size can be corrected only by end face polishing described later).
- the coring may be performed on the central portion that becomes a circular hole instead of the scribing process.
- a cutting line can be suitably provided using a scriber.
- a scriber may not follow surface unevenness
- 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 the inner peripheral end of the ring-shaped glass with a diamond grindstone.
- the end face of the disk-shaped glass is polished.
- the inner peripheral side end surface and the outer peripheral side end surface of the glass are mirror-finished by brush polishing.
- 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 dust attached to the end surface of glass, damage or scratches by performing end face polishing Can do.
- first polishing is performed on the main surface of the 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 ⁇ m to 10 ⁇ m. 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.
- 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.
- 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.
- a plurality of disk-shaped glasses are held in each polishing carrier.
- 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 And the main surfaces of the front and back surfaces of the disk-shaped glass are polished.
- a hard resin polisher is used as the polishing pad, and for example, cerium oxide abrasive grains are used as the abrasive.
- the disc-shaped glass after the first polishing is chemically strengthened.
- a molten salt of potassium nitrate can be used as the chemical strengthening solution.
- the chemical strengthening solution 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 solution, for example, 3 hours to 4 hours. Soaked.
- the immersion is preferably performed in a state of being accommodated in a holder so that a plurality of glasses are held at the end faces so that both the main surfaces of the glass are chemically strengthened.
- the glass is strengthened and has good impact resistance.
- the chemically strengthened glass is washed. For example, after washing with sulfuric acid, it is washed with pure water, IPA (isopropyl alcohol) or the like.
- second polishing is performed on the glass that has been chemically strengthened and thoroughly cleaned.
- the machining allowance by the second polishing is, for example, about 1 ⁇ m.
- the second polishing is intended to finish the main surface in a mirror shape.
- 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.
- 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.
- a soft foamed resin polisher is used as the polishing pad, and as the abrasive, for example, cerium oxide abrasive grains or colloidal silica that are finer than the cerium oxide abrasive grains used in the first polishing step are used.
- the disc-shaped glass polished in the second polishing step is washed again.
- a neutral detergent, pure water, and IPA are used.
- a glass substrate for a magnetic disk having a main surface flatness of 4 ⁇ m or less (within 4 ⁇ m) and a main surface roughness (Ra) of 0.2 nm or less is obtained.
- each layer such as a magnetic layer is formed on the glass substrate for magnetic disk to produce a magnetic disk.
- the chemical strengthening step is performed between the first polishing step and the second polishing step, but is not limited to this order.
- the chemical strengthening step can be appropriately arranged.
- the order of the first polishing process, the second polishing process, and the chemical strengthening process (hereinafter, process order 1) may be used.
- the process order 1 since the surface unevenness
- the flatness of the glass blank used for processing and the flatness of the produced magnetic recording medium glass substrate can be made substantially the same.
- the flatness required for the magnetic recording medium glass substrate is recently required to be 10 ⁇ m or less (within 10 ⁇ m) for a 2.5-inch glass substrate, for example. This is because it can be easily achieved by the glass blank produced by the glass blank production method of the present embodiment.
- “the flatness of the glass blank used for processing and the flatness of the produced magnetic recording medium glass substrate are substantially the same” means that the required magnetic recording medium glass substrate (glass substrate for magnetic disk) ) Is 100%, it means that the flatness of the glass blank is 105% or less.
- the process is carried out mainly for improving flatness such as a lapping process. Can be omitted.
- the magnetic recording medium manufacturing method of the first embodiment is a magnetic recording layer in which a magnetic recording layer is formed on a magnetic recording medium glass substrate manufactured by the magnetic recording medium glass substrate manufacturing method of the first embodiment.
- a magnetic recording medium is manufactured through at least a forming step.
- Magnetic recording media are called magnetic disks, hard disks, etc., internal storage devices (such as fixed disks) such as desktop computers, server computers, notebook computers, and mobile computers, and portable recording and playback that records and plays back images and / or audio. It is suitable for an internal storage device of a device, an in-vehicle audio recording / reproducing device, and the like.
- an adhesion layer, an underlayer, a magnetic layer (magnetic recording layer), a protective layer, and a lubricating layer are stacked on the main surface of a magnetic recording medium glass substrate in order from the side closer to the main surface.
- a magnetic recording medium glass substrate is introduced into a depressurized film forming apparatus, and an adhesion layer to a magnetic layer are sequentially formed on the main surface of the magnetic recording medium glass substrate in an Ar atmosphere by a DC magnetron sputtering method.
- CrTi can be used as the adhesion layer
- CrRu can be used as the underlayer.
- the size of the magnetic recording medium is not particularly limited, but since the magnetic recording medium glass substrate is made of a glass material with excellent impact resistance, it is convenient to carry and may be exposed to external impacts. A size of 2.5 inches or less is preferred.
- the method for producing a glass blank for a magnetic recording medium glass substrate according to the second embodiment refers to a molten glass lump that is falling.
- a glass blank for a magnetic recording medium glass substrate hereinafter, “ May be abbreviated as “glass blank.”.
- the press molding process brings the first press mold and the second press mold close to each other until the guide member of the first press mold and the second press mold come into contact with each other. Press molding of the first press mold with the first step of molding the molten glass lump into sheet glass, the first press mold guide member, and the second press mold And a second step of further pressing the sheet glass with the mold body and the second press mold.
- the first press mold and the second press mold are brought close to each other. For this reason, a molten glass lump is press-molded by the first press-molding die and the second press-molding die to form a plate glass. Further, by bringing the first press mold and the second press mold close to each other, the guide member of the first press mold and the second press mold are brought into contact with each other. Therefore, at this time, the distance between the press molding surfaces of the first press mold and the second press mold is kept substantially constant. For this reason, the plate
- the flatness of the glass blank can be improved by cooling the plate glass while preventing both of the plate glass from being deformed in a state where both surfaces of the plate glass are supported by the press-molded surface, and the fluidity is lowered or lost. This is because it is considered that deterioration can be suppressed.
- the glass sheet in contact with the press molding surface shrinks in the process of being deprived of heat by the press mold and being cooled. For this reason, if the distance between the press molding surfaces immediately after the completion of the first step is maintained thereafter, a gap is formed between the press molding surface and the sheet glass. Therefore, considering the shrinkage of the plate glass, it is difficult to always support both sides of the plate glass with the press-molded surface. Therefore, even if the state where the guide member of the first press mold and the second press mold are kept in contact with each other for a while after the first step is finished, It is difficult to suppress deformation.
- the press mold body of the first press mold and the second press mold Continue pressing the glass sheet with the mold. That is, the sheet glass is further pressed so that only the press mold body of the first press mold is brought closer to the press molding surface side of the second press mold. For this reason, even if the plate-like glass contracts in the thickness direction, the press-molding surface is kept in close contact with both sides of the plate-like glass without any gap, and supports both sides of the plate-like glass.
- the sheet glass is cooled in such a state that the both sides of the sheet glass are always supported by the press-molded surface and taken out after the fluidity is reduced or lost, the flatness of the glass blank is further deteriorated. It can be reliably suppressed.
- the press molding surface of the press mold composed of a solid member having higher thermal conductivity than the gas such as air existing in the gap and the plate glass are kept in close contact with each other without any gap, so that the plate shape Glass heat is efficiently taken away by the press mold.
- liquidity of the sheet glass during press molding is accelerated
- the first press mold may be provided with at least a press mold body and a guide member.
- the second press mold for example, a press mold having a columnar body with one end surface constituting the press mold surface can be used.
- the guide member of the first press mold contacts the press molding surface of the second press mold.
- the press mold body of the first press mold in a state where the guide member of the first press mold and the press molding surface of the second press mold are in contact, the press mold body of the first press mold, The sheet glass is further pressed by the second press mold (hereinafter, such a press molding process may be referred to as a “first press process”).
- each of the first press mold and the second press mold includes a press mold body having a press molding surface, and press molding at the time of press molding.
- the first press mold and the second press mold are brought into contact with a part of the press mold disposed opposite to the press molding surface when being extruded to the side of the press mold disposed opposite to the surface.
- the first step is to move the first press mold and the second press mold until the first press mold guide member and the second press mold guide member contact each other. This is done by bringing them closer together.
- the second step is a state where the first press mold die guide member and the second press mold guide member are in contact with each other. It is carried out by further pressing the sheet glass with the press mold body of the second press mold (hereinafter, such a press molding process may be referred to as a “second press process”). .
- a press mold including at least a press mold main body and a guide member used in both the first press process and the second press process is a press mold main body. It is particularly preferable that the guide member has a function of being able to move separately to the other press-molding die disposed opposite to the guide member.
- the glass blank manufacturing method of the second embodiment can be carried out by any of the first press process and the second press process.
- the time required for press molding can be further shortened with respect to the first press process, for example, about 1/3.
- the second pressing process is performed from the viewpoint of enabling this. This is because the structure of the pair of press molds used in the second press process is more similar or the same in the second press process than in the first press process, so that the position is between the pair of molds. This is because the cooling of the sheet glass to be performed can be performed more symmetrically from both sides.
- the method for producing a glass blank of the second embodiment described above is not particularly limited as long as it includes at least a press molding step, but it is usually preferable to have a molten glass lump forming step.
- a take-out step of taking out the sheet glass by separating the first press mold and the second press mold is performed.
- a molten glass lump that is an object of press molding is produced.
- a method for producing a molten glass lump usually, by dropping the molten glass from the glass outlet and cutting the tip of the molten glass flow that continuously flows out downward in the vertical direction, A molten glass lump is formed.
- a pair of shear blades can be used for cutting the tip of the molten glass flow.
- the viscosity of the molten glass is not particularly limited as long as it is suitable for cutting of the tip portion or press molding, but is usually controlled to a constant value within a range of 500 dPa ⁇ s to 1050 dPa ⁇ s. It is preferable.
- the viscosity of the molten glass lump immediately before press molding is also within the above range.
- a molten glass flow 120 is provided from a glass outlet 112 provided at the lower end of a molten glass outflow pipe 110 whose upper end is connected to a molten glass supply source (not shown). Is continuously discharged downward in the vertical direction.
- the first shear blade (lower blade) 130 and the second shear blade (upper blade) 140 are melted on both sides of the molten glass flow 120, respectively. It arrange
- the lower blade 130 and the upper blade 140 are each orthogonal to the central axis D, and in the drawing, are orthogonal to the direction of the arrow X1 that proceeds from the left side to the right side, and the central axis D. And by moving to the arrow X2 direction which progresses from the right side to the left side in the figure, it approaches from the both sides of the molten glass flow 120 to the front-end
- the viscosity of the molten glass flow 120 is controlled by adjusting the temperature of the molten glass outflow pipe 110 or the molten glass supply source upstream thereof.
- the lower blade 130 and the upper blade 140 are provided on the substantially plate-like main body portions 132 and 142 and the end portions of the main body portions 132 and 142, and the molten glass flow that continuously flows downward in the vertical direction. It has blade parts 134 and 144 which cut 120 front-end
- the upper surface 134U of the blade portion 134 and the lower surface 144B of the blade portion 144 form a surface that substantially matches the horizontal plane, and the lower surface 134B of the blade portion 134 and the upper surface 144U of the blade portion 144 intersect with the horizontal plane.
- An inclined surface is formed.
- the lower blade 130 and the upper blade 140 are arranged so that the upper surface 134U of the blade portion 134 and the lower surface 144B of the blade portion 144 are at substantially the same height with respect to the vertical direction.
- the lower blade 130 and the upper blade 140 are further moved in the directions of the arrow X1 and the arrow X2, respectively, so that the upper surface 134U of the blade portion 134 and the lower surface 144B of the blade portion 144 are obtained.
- the lower blade 130 and the upper blade 140 penetrate into the molten glass flow 120 up to the vicinity of the central axis D, and the tip portion 122 is cut as a substantially spherical molten glass lump 124.
- first step the first press mold and the second press mold in which the molten glass lump 124 shown in FIG. 13 is arranged to face each other in the direction intersecting the falling direction of the molten glass lump 124.
- first press mold and the second press mold are opposed to each other in a direction substantially perpendicular to the falling direction of the molten glass lump 124 so as to form an angle of 90 ° ⁇ 1 °. It is particularly preferable that they are disposed so as to face each other in a direction orthogonal to the falling direction of the molten glass lump 124.
- the temperature of the press molding surfaces of the first press mold and the second press mold immediately before the first step is added to the strain point of the glass material constituting the molten glass lump 124 by 10 ° C. It is preferable that the temperature is not higher than the temperature obtained by adding 5 ° C. to the strain point of the glass material constituting the molten glass lump 124.
- the lower limit value of the temperature of the press molding surfaces of the first press mold and the second press mold immediately before the first step is not particularly limited, but the glass by rapid cooling of the molten glass lump 124 is not limited.
- the absolute value of the difference between the temperature of the press molding surface of the first press mold and the temperature of the press molding surface of the second press mold immediately before the first step is performed is 0 ° C. to 10 ° C. Is preferably in the range of 0 ° C., more preferably in the range of 0 ° C. to 5 ° C., and particularly preferably 0 ° C. In this case, it is possible to more reliably suppress the occurrence of a temperature difference between both sides of the plate glass formed into a plate shape by pressing the molten glass lump 124, and as a result, the flatness can be further improved.
- the absolute value of the in-plane temperature difference between the press forming surfaces of the first press mold and the second press mold immediately before the first step is performed is in the range of 0 ° C. to 100 ° C. Is preferably in the range of 0 ° C. to 50 ° C., particularly preferably 0 ° C.
- the “in-plane temperature of the press-molded surface” means a temperature measured in the maximum region where the press-molded surface and the molten glass lump 124 drawn into a plate shape come into contact with each other during press molding.
- the molten glass lump 124 shown in FIG. 13 includes a first press mold 150 and a second press that are arranged to face each other in a direction perpendicular to the falling direction Y1 of the molten glass lump 124. It enters between the molds 160.
- the first press mold 150 and the second press mold 160 before the press molding are arranged symmetrically with respect to the falling direction Y1 and spaced apart from each other in the orthogonal direction. ing.
- the first press mold 150 is moved in the direction of the arrow X1 perpendicular to the falling direction Y1 and proceeds from the left side to the right side in the figure
- the second press mold 160 is It moves in the direction of the arrow X2 that is orthogonal to the falling direction Y1 and proceeds from the right side to the left side in the figure.
- the moving speed of the first press mold 150 in the arrow X1 direction and the moving speed of the second press mold 160 in the arrow X2 direction are set to be the same or substantially the same.
- the press molds 150 and 160 include press mold main bodies 152 and 162 having a substantially disk shape, and guide members 154 and 164 disposed so as to surround the outer peripheral ends of the press mold main bodies 152 and 162.
- FIG. 14 is a cross-sectional view, the guide members 154 and 164 are drawn so as to be positioned on both upper and lower sides of the press mold main bodies 152 and 162 in FIG. Further, the description of the drive member that moves the press mold 150 in the direction of the arrow X1 and moves the press mold 160 in the direction of the arrow X2 is omitted in the drawing.
- One surface of the press mold main bodies 152 and 162 is the press molding surfaces 152A and 162A.
- the first press mold 150 and the second press mold 160 are opposed to each other so that the press molding surfaces 152A and 162A face each other.
- the guide member 154 is provided with a guide surface 154A at a height position slightly projecting in the X1 direction with respect to the press molding surface 152A, and the guide member 164 is slightly in the X2 direction with respect to the press molding surface 162A.
- a guide surface 164A is provided at a height position protruding only.
- this gap thickness is the thickness of the molten glass lump 124 that is press-molded between the first press mold 150 and the second press mold 160, that is, the thickness of the glass blank.
- the press molding surfaces 152A and 162A are obtained by performing the first step so that the molten glass lump 124 has the press molding surface 152A of the first press molding die 150 and the press molding surface 162A of the second press molding die 160.
- the entire press molding surface 152A including the molten glass stretching region S1 and the press molding surface 162A including the molten glass stretching region S2 are generally flat with substantially zero curvature. Make up.
- the flat surface has only minute unevenness formed by performing normal flattening processing or mirror polishing processing when manufacturing a press mold, and is larger than these minute unevenness. There are no protrusions and / or recesses.
- the glass blank is manufactured by pressing the molten glass lump 124 by pressing it with the press molding surfaces 152A and 162A. For this reason, the surface roughness of the press molding surfaces 152A and 162A and the surface roughness of the main surface of the glass blank are substantially equal.
- the surface roughness (centerline average roughness Ra) of the main surface of the glass blank is 0.01 to 10 ⁇ m when performing scribing performed as a post-process described later and grinding using a diamond sheet. Since it is desirable to set the range, the surface roughness (centerline average roughness Ra) of the press-molded surface is also preferably in the range of 0.01 to 10 ⁇ m.
- the molten glass lump 124 shown in FIG. 14 further falls downward and enters between the two press-molding surfaces 152A and 162A. Then, as shown in FIG. 15, when the press molding surfaces 152A and 162A that are parallel to the falling direction Y1 reach the vicinity of the substantially central portion in the vertical direction, both side surfaces of the molten glass lump 124 are pressed to the press molding surfaces 152A and 152A, Contact 162A. At this time, it is preferable that the press molding surface 152A and the press molding surface 162A are brought into contact with the molten glass lump 124 substantially simultaneously as shown in FIG.
- substantially simultaneously contact means that the absolute value of the time difference between the time when the molten glass block and one press-molded surface are in contact with the point when the molten glass block and the other press-formed surface are in contact with each other. It means within 0.1 seconds.
- the absolute value of this time difference is more preferably within 0.05 seconds, and most preferably 0 seconds (simultaneous).
- the time required for the molten glass lump to contact the upper press forming surface after the molten glass lump contacts the upper press forming surface depends on the press forming conditions. Although it depends, it is generally about 1.5 to 3 seconds.
- the press molding surface 152A and the press molding surface 162A are brought into contact with the molten glass lump 124 substantially simultaneously, and at least during the execution of the press molding process, the first press molding is performed. It is preferable that the temperature of the press molding surface 152A of the mold 150 is substantially the same as the temperature of the press molding surface 162A of the second press molding die 160. Thereby, both surfaces of the molten glass lump 124 being formed into a plate shape in the first step and the plate glass sandwiched between the pair of press molds 150 and 160 in the second step are always maintained. It will continue to be cooled symmetrically.
- the absolute value of the temperature difference between the temperature of the press molding surface 152A of the first press mold 150 and the temperature of the press molding surface 162A of the second press mold 160 is the same. It means that it is within 10 ° C.
- the absolute value of this temperature difference is more preferably within 5 ° C, most preferably 0 ° C.
- the “temperature of the press molding surface” means a temperature near the center of the press molding surface.
- the absolute value of the temperature difference between the upper mold press surface and the lower mold press surface during the press molding of the molten glass lump is also determined by the press molding conditions. However, it is generally about 50 ° C to 100 ° C.
- the drop distance is It is preferable to select within the range of 1000 mm or less, more preferable to select within the range of 500 mm or less, further preferable to select within the range of 300 mm or less, and most preferable to select within the range of 200 mm or less. .
- the lower limit of the drop distance is not particularly limited, but is preferably 100 mm or more for practical use.
- the “fall distance” is the moment when the tip 122 is separated as the molten glass lump 124 as illustrated in FIG.
- the position of the press molding start time (instant of the press molding start) as illustrated in FIG. 15, that is, the distance to the vicinity of the substantially central portion in the diameter direction of the press molding surfaces 152A and 162A parallel to the falling direction Y1. means.
- the molten glass lump 124 is continuously pressed from both sides by the first press mold 150 and the second press mold 160, the molten glass lump 124 is separated from the molten glass lump 124.
- the press-molded surfaces 152A and 162A are spread with a uniform thickness around the position where they first contact.
- the pressing surfaces 152A and 162A are pressed by the first press mold 150 and the second press mold 160 until the guide surfaces 154A and 164A come into contact with each other. In between, it is formed into a disk-like or substantially disk-like plate-like glass 126.
- the plate-like glass 126 shown in FIG. 17 has substantially the same shape and thickness as the finally obtained glass blank. And the size and shape of both surfaces of the sheet glass 126 correspond with the size and shape of molten glass extending
- the guide surface 154A and the guide surface 164A are in contact with each other, so that it is easy to maintain the parallel state between the press molding surface 152A and the press molding surface 162A.
- the minimum of press molding time is not specifically limited, It is preferable that it is 0.05 second or more practically.
- the press mold 150 has a press mold body 152 and a guide member 154, and the press mold 160 has the same structure.
- the press mold main body 152 and the guide member 154 move simultaneously and integrally in the direction of the arrow X1, and the press mold main body 162 and the guide member 164 simultaneously and integrally move. Move in the direction of arrow X2.
- the press molds 150 and 160 have guide members 154 and 164, respectively, when the guide member 154 and the guide member 164 are in contact with each other as shown in FIG. 17, the press mold surface 152A and the press mold surface 162A Are kept parallel. Therefore, as shown in FIGS. 14 to 16, in the process in which the press mold 150 is moved in the direction of the arrow X1 and the press mold 160 is moved in the direction of the arrow X2, the press mold surface 152A and the press mold surface 162A are Even if the parallel state cannot be maintained, it is easy to make the thickness deviation of the obtained glass blank very small. Therefore, in the drive device for driving the press molds 150 and 160, the press molding surface 152A and the press molding surface 162A always maintain an accurate parallel state in the series of processes shown in FIGS. The precise control ability to control is not required.
- the first press mold 150 is in a state where the guide member 154 of the first press mold 150 and the guide member 164 of the second press mold 160 are in contact with each other.
- the press mold body 152 of the second press mold 160 is driven to move in the direction of arrow X1
- the press mold body 162 of the second press mold 160 is driven to move in the direction of arrow X2.
- the plate glass 126 is further pressed by the press mold main bodies 152 and 162.
- the glass sheet 126 immediately after finishing the first step has high temperature and high fluidity (low viscosity). That is, the plate glass is very easily deformed and the flatness is likely to deteriorate. For this reason, if the cooling of the plate glass 126 does not proceed so much and the second step is completed while maintaining a highly fluid state, the plate glass 126 is deformed after the second step is completed, and the glass blank The flatness of the may deteriorate. Therefore, the second step is preferably continued until the temperature of the sheet glass 126 becomes at least a temperature obtained by adding 10 ° C. to the strain point of the glass material constituting the sheet glass 126. That is, while maintaining the state immediately after the completion of the first step shown in FIG.
- the cooling of the glass sheet 126 proceeds sufficiently, the fluidity is lost, and the glass sheet 126 is continuously pressed to a temperature range where deformation is practically impossible. That is, the sheet glass 126 can be solidified while maintaining the state in which the deformation of the sheet glass 126 immediately after the first step is completed. Therefore, the flatness of the produced glass blank can be made more excellent.
- the duration of the second step is preferably controlled such that the flatness of the glass blank is 10 ⁇ m or less (within 10 ⁇ m), and the flatness of the glass blank is 4 ⁇ m or less (within 10 ⁇ m). More preferably, it is controlled. If the duration time of the second step is short, distortion occurs in the sheet glass 126 in the cooling process due to disturbance, and the distortion easily deteriorates the flatness of the glass blank. Therefore, the duration of the second step is changed, the flatness of the obtained glass blank is measured, and as a result, the duration of the second step is set so that the flatness is 10 ⁇ m or less (within 10 ⁇ m). It is preferable to manufacture a glass blank.
- the duration of the second step may be set in consideration of the flatness and productivity of the glass blank. From these viewpoints, the duration of the second step is specifically preferably in the range of 2 to 40 seconds, and preferably in the range of 2 to 30 seconds.
- the second step in order to control the flatness of the glass blank to 10 ⁇ m or less (within 10 ⁇ m), in the second step, the flowability of the sheet glass is lost, up to a temperature range where deformation is virtually impossible, It is particularly preferred to select the duration of the second step so as to keep pressing the glass sheet. In this case, the sheet glass 126 can be solidified while maintaining the state in which the deformation of the sheet glass 126 immediately after the first step is completed. Therefore, the flatness of the produced glass blank can be made more excellent.
- the duration of the second step is such that the temperature of the sheet glass at the end of the second step is equal to or lower than the temperature obtained by adding 10 ° C. to the strain point of the glass material constituting the sheet glass.
- the lower limit temperature of the temperature of the sheet glass at the end of the second step is not particularly limited, but from the viewpoint of suppressing a decrease in productivity due to an increase in time required to perform the second step, practically, It is preferable that the strain point or higher. Therefore, it is preferable that the upper limit value of the duration time in the second step is also selected from this viewpoint.
- the press molding surface 152A and 162A are between the time when the second step is completed.
- the temperature of the glass (molten glass lump 124 and plate-like glass 126) positioned in between is generally about 1200 ⁇ 50 ° C. to about 480 ° C. ⁇ 20 ° C., depending on the glass material used for press molding. Will drop significantly. Therefore, in the second step, thermal contraction in the radial direction of the sheet glass 126 proceeds with such a significant decrease in temperature.
- Such thermal shrinkage reaches a temperature range in which the temperature of the sheet glass 126 is lower, in particular, a temperature range equal to or lower than the temperature obtained by adding 10 ° C. to the strain point of the glass material constituting the sheet glass 126. It becomes more remarkable when the second step is continued.
- the press-molded surfaces 152A and 162A that are in contact with both surfaces of the sheet glass 126 continue to absorb the heat of the sheet glass 126 and thermally expand in the plane direction, or the sheet glass It is considered that the thermal expansion in the planar direction is stopped or the heat is gradually contracted by absorbing sufficient heat from 126.
- the second step there is a difference in the degree of thermal expansion / contraction between both members between the both surfaces of the sheet glass 126 and the press molding surfaces 152A, 162A. For this reason, in the second step, on both surfaces of the sheet glass 126 that is undergoing heat shrinkage, the force to extend in the radial direction of the sheet glass 126 by the press molding surfaces 152A, 162A, that is, heat A force in the direction opposite to the contraction acts. However, in the second step, the fluidity of the sheet glass 126 decreases with the progress of the second step. Therefore, if excessive stress acts on the sheet glass 126, the sheet glass 126 is likely to be brittle fractured. . For this reason, if a force in the direction opposite to the thermal contraction always acts on both surfaces of the plate glass 126, excessive stress acts in the plane direction of the plate glass 126, and the plate glass 126 is broken. Become.
- the press pressure decreases with time is not only the case where the press pressure decreases with the passage of time in the second step, but also the press pressure temporarily with respect to the passage of time. Even when increasing or maintaining a constant value, when the change in the press pressure with respect to time is approximated by a linear equation, the case where the slope becomes negative is also included. Further, the press pressure may be decreased stepwise with the passage of time, or may be continuously decreased with the passage of time.
- the temperature of the sheet glass 126 held between the first press mold 150 and the second press mold 160 is reduced. It is preferable that the glass material constituting the plate-like glass 126 is decreased when it falls within the range of the yield point ⁇ 30 ° C. Thereby, the crack of the plate-like glass 126 can be more effectively suppressed by a relatively simple operation of the pressing pressure.
- the pressing pressure is assumed to be 1% to 60% after reduction, assuming that 100% before reduction. It is preferable to be in the range of about%.
- the first press mold 150 and the second press mold 160 are separated and sandwiched between the first press mold 150 and the second press mold 160.
- the extraction process which takes out the plate-shaped glass 126 which performed is performed.
- This extraction step can be performed, for example, as described below.
- the first press mold 150 is moved in the direction of the arrow X2 so that the first press mold 150 and the second press mold 160 are separated from each other.
- the press mold 160 is moved in the arrow X1 direction. Thereby, the press molding surface 162A and the plate-like glass 126 are released.
- FIG. 1 the first press mold 150 and the second press mold 160 are separated and sandwiched between the first press mold 150 and the second press mold 160.
- the press molding surface 152A and the plate glass 126 are released from the mold, and the plate glass 126 is dropped to the lower side Y1 in the vertical direction and taken out.
- the release can be performed such that the plate glass 126 is peeled off by applying a force from the outer peripheral direction of the plate glass 126. In this case, the sheet glass 126 can be taken out without applying a large force.
- the press molding surface 162A and the plate glass 126 may be released.
- the extracted plate-like glass 126 is annealed as necessary to reduce and remove the distortion, thereby obtaining a base material for processing the magnetic recording medium glass substrate, that is, a glass blank.
- the glass blank obtained by the glass blank manufacturing method of the second embodiment described above can have a flatness of, for example, 10 ⁇ m or less (within 10 ⁇ m), and 4 ⁇ m or less (within 4 ⁇ m). It is also very easy to do.
- the flatness is preferably 4 ⁇ m or less (within 4 ⁇ m) from the viewpoint of omitting or shortening post-processes performed mainly for improving flatness such as a lapping process.
- the manufacturing method of the glass blank of 2nd this embodiment is suitable for manufacture of a glass blank with thinner plate thickness and good flatness. Specifically, it is suitable for manufacturing a glass blank having a plate thickness of 2 mm or less and a flatness of 10 ⁇ m or less (within 10 ⁇ m). A more preferable plate thickness is 1.5 mm or less, a further preferable plate thickness is 1.2 mm or less, and a still more preferable plate thickness is 1.0 mm or less.
- the press mold 150 used in the glass blank manufacturing method of the second embodiment has at least a press mold body 152 and a guide member 154.
- the press mold 160 also has at least a press mold body 162 and a guide member 164 and has the same structure as the press mold 150.
- the press mold 150 will be described as an example.
- the press mold 150 is configured as a separate member from the press mold main body 152 and the guide member 154. For this reason, in the first step, the press mold main body 152 and the guide member 154 can be integrally driven so as to be pushed out toward the press mold 160 arranged opposite to each other, and in the second step.
- a press mold without the guide member 154 can be used.
- this type of press mold even after the molten glass lump 124 is press-molded into a sheet glass 126, both surfaces of the sheet glass 126 are always closely adhered to and supported by the press-molding surfaces 152A and 162A. be able to.
- the guide members 154 and 164 do not exist, it is difficult to press-mold the press-molding surface 152A and the press-molding surface 162A accurately in parallel with each other unless the press-molding die is driven very precisely. For this reason, the plate
- the press mold 150 (and the press mold 160) having at least the guide member 154 and the press mold body 152 configured as separate members have a thickness variation and flatness of the glass blank. It is extremely advantageous in that both of the properties can be improved in a balanced manner.
- the heat resistance temperature of the metal or alloy constituting the press molds 150 and 160 is preferably 1000 ° C. or higher, and more preferably 1100 ° C. or higher.
- the materials constituting the press molds 150 and 160 are preferably spheroidal graphite cast iron (FCD), alloy tool steel (such as SKD61), high speed steel (SKH), cemented carbide, colmonoy, stellite, and the like.
- the press molds 150 and 160 may be cooled using a cooling medium such as water or air to suppress an increase in the temperature of the press molds 150 and 160. Further, in order to make the temperature distribution in the surfaces of the press molding surfaces 152A and 162A uniform, the vicinity of the center of the press molding surfaces 152A and 162A is cooled using a cooling medium, and / or the press molding die 150 is used. , 160 may be arranged on the outer peripheral side of the heater 160 to heat the outer edge side of the press molding surfaces 152A, 162A.
- a cooling medium such as water or air
- region (molten glass extending
- the surface may have a surface on which a large uneven portion such as a protrusion for forming a V-shaped groove having a depth of about 1/3 to 1/4 of the plate thickness is formed. A surface is preferred.
- the entire pressing surfaces 152A and 162A may be substantially flat. This is because when a large V-shaped groove is formed in the glass blank, crack defects presumed to be caused by stress concentration in the V-shaped groove portion are likely to occur.
- the “substantially flat surface” means a surface having a very small curvature such as a slight convex surface or a concave surface in addition to a normal flat surface having substantially zero curvature.
- the “substantially flat surface” has minute irregularities formed by performing a normal flattening process or a mirror polishing process when manufacturing a press mold.
- larger protrusions and / or recesses may be provided as necessary as compared with the minute unevenness.
- the convex portion larger than the minute irregularities is substantially point-like having a height of 20 ⁇ m or less with a small possibility of causing deterioration of flow resistance or promoting partial cooling of the molten glass lump. And / or a substantially linear protrusion is acceptable.
- the height is preferably 10 ⁇ m or less, and more preferably 5 ⁇ m or less.
- the convex portion larger than the minute unevenness is not substantially punctiform and substantially linear, and the convex shape is a trapezoidal shape with a minimum width of the top surface of several millimeters or more, or
- the height is allowed to be 50 ⁇ m or less.
- the height is preferably 30 ⁇ m or less, and more preferably 10 ⁇ m or less.
- the side surface of the trapezoidal convex portion has an inclination angle of 0.5 with respect to the top surface. It is preferable to form a plane that forms an angle of less than or equal to a degree, or a curved surface with this plane as a concave surface. The angle is more preferably 0.1 degrees or less.
- the recesses larger than the minute unevenness are substantially point-like and / or less than 20 ⁇ m in depth so as not to deteriorate the fluidity of the molten glass flowing into the recesses during press molding. Or if it is a substantially linear recessed part, it is accept
- the depth is preferably 10 ⁇ m or less, and more preferably 5 ⁇ m or less.
- the concave portion larger than the minute unevenness is not substantially punctiform or substantially linear, and the concave portion having an inverted trapezoidal shape with a minimum width of the top surface of several millimeters or more, or
- the depth is 50 ⁇ m or less. If that is acceptable.
- the depth is preferably 30 ⁇ m or less, and more preferably 10 ⁇ m or less.
- the inclination angle of the side surface of the trapezoidal convex portion is 0.5 degrees with respect to the bottom surface. It is preferable to form a plane having the following angle, or a curved surface with this plane as a concave surface. The angle is more preferably 0.1 degrees or less.
- the press mold 150 (and the press mold 160) includes at least a press mold body 152 and a guide member 154, and includes a first step and a second step.
- the specific structure is not particularly limited.
- the first extrusion member and the second extrusion member are further provided. It is preferable.
- the first extruding member is a side of the press mold 160 where the press mold body 152 and the guide member 154 are orthogonal to the press mold surface 152A and are opposed to the press mold surface 152A. And at least a function of extruding at the same time.
- the second extrusion member is pressed by the first extrusion member after the guide member 154 comes into contact with a part of the press molding die 160 (the guide member 164) arranged to face the press molding surface 152A.
- the main body 152 has at least a function of pushing out the main body 152 toward the press molding die 160 in a direction orthogonal to the press molding surface 152A and arranged to face the press molding surface 152A.
- FIG. 20 is a schematic cross-sectional view showing an example of a press mold used in the method for manufacturing a glass blank for a magnetic recording medium glass substrate according to the second embodiment. It is a figure which shows an example of a more concrete structure.
- the press mold 150S shown in FIG. 20 corresponds to the press mold 150, but the press mold 160 can employ the same structure.
- the main part of the press mold 150 ⁇ / b> S includes a press mold main body 152, a guide member 154, a first push member 156, and a second push member 158.
- the central axes of the respective members coincide with each other, and the central axes substantially coincide with the horizontal direction.
- the press mold main body 152 is formed of a cylindrical body having one end surface constituting a circular press molding surface 152A.
- the shape of the press mold main body 152 is a columnar shape in the example shown in FIG. 20, but the shape is not particularly limited as long as it is a substantially columnar shape.
- the press molding surface 152A forms a substantially flat surface.
- the guide member 154 has a length in the axial direction X that is longer than a length in the axial direction X of the press-molding die main body 152 made of a cylindrical body, and accommodates the press-molding die main body 152 on the inner peripheral side.
- one end face (guide face 154A) is formed of a cylindrical body that comes into contact with a guide member (not shown in the drawing) constituting the other press mold.
- the difference between the length of the guide member 154 and the length of the press mold body 152 in the axial direction X in other words, the height difference H between the guide surface 154A and the press molding surface 152A in the axial direction X is the glass to be produced. This corresponds to approximately half the blank thickness.
- the shape of the guide member 154 is cylindrical, but the shape is not particularly limited as long as it is cylindrical.
- the first extruding member 156 is composed of a disk-shaped member.
- one surface (extruded surface 156A) of the disk-shaped first extruding member 156 has the other end surface (extruded surface 152B) of the press mold main body 152 and the other end surface (extruded surface) of the guide member 154. It consists of a flat surface in contact with the surface 154B).
- a through hole 156 ⁇ / b> H that penetrates in the thickness direction of the first push member 156 is provided in a part of a region facing the extruded surface 152 ⁇ / b> B of the press mold main body 152.
- the surface 156B opposite to the extrusion surface 156A is connected to a first driving device (not shown). For this reason, during press molding, the first driving device simultaneously presses the press mold main body 152 and the guide member 154 through the first extruding member 156 in the axial direction X in the drawing. It can be extruded from the side where the member 156 is arranged to the side where the press mold main body 152 and the guide member 154 are arranged.
- the shape of the first push member 156 is a disc shape, but the shape is not particularly limited as long as it is substantially plate-shaped.
- the through hole 156H is provided as a hole having a circular opening along the center axis X of the press mold main body 152 and the first extrusion member 156, but the extruded surface 152B of the press mold main body 152 is provided. Any number of through holes 156H can be provided at any position of the first pushing member 156 as long as it is a part of the region facing the. Moreover, the opening shape of the through hole 156H can also be selected as appropriate. However, it is particularly preferable that the through hole 156H is provided point-symmetrically with respect to the central axis X of the press mold main body 152.
- the second extruding member 158 is disposed in the through hole 156H and is composed of a rod-like member connected to the extruded surface 152B side of the press mold main body 152.
- the second push member 158 has a cylindrical bar shape, but the shape is not particularly limited as long as the press mold main body 152 can be moved in the X-axis direction.
- the end opposite to one end connected to the extruded surface 152B side of the second pushing member 158 is connected to a second driving device (not shown).
- the second drive unit allows only the press mold main body 152 to be inserted from the side where the second extruding member 158 is disposed via the second extruding member 158. It can be extruded along the X-axis direction to the side where 152 is disposed.
- the temperature distribution in the surface of the press molding surface 152A can be controlled to be uniform in order to make it easy to stretch the molten glass lump 124 thinly and uniformly.
- a heating member for heating the vicinity of the outer edge side of the press molding surface 152A is provided, and / or (2) the inside of the press mold main body 152 and the press molding surface 152A side.
- a flow path through which the cooling medium flows can be provided at least near the center.
- the heating member for example, a cylindrical heater is disposed on the outer peripheral side of the guide member 154, or a rod-shaped heater parallel to the axial direction X is equally spaced along the circumferential direction of the guide member 154. Can be arranged. These heaters may be built in the guide member 154 or may be arranged so as to be embedded on the outer peripheral surface side of the press mold main body 152.
- the cooling liquid a liquid such as water, a gas such as air, a gas dispersed by spraying a liquid, or the like can be used.
- FIG. 21 is a schematic cross-sectional view showing another example of a press mold used in the method for manufacturing a glass blank for a magnetic recording medium glass substrate according to the second embodiment. 21 that have substantially the same or similar functions as those shown in FIG. 20 are denoted by the same reference numerals.
- the main part of the press mold 200 shown in FIG. 21 includes a press mold body 152, a guide member 154, a first push member 156, and a second push member 158. Yes.
- the central axes of the respective members coincide with each other, and the central axes substantially coincide with the horizontal direction.
- the press mold 200 shown in FIG. 21 and the press mold 150S shown in FIG. 20 include a press mold body 152, a guide member 154, a first push member 156, and a second push member 158.
- the following points are largely different. That is, compared with the press mold 150S shown in FIG. 20, in the press mold 200 shown in FIG.
- the press mold main body 152 and the guide member 154 include the outer peripheral surface of the press mold main body 152 and the guide member 154.
- the press-molding die main body 152 and the first extrusion member 156 are arranged so that the surface to be extruded 152B of the press-molding die main body 152 and the first extrusion
- the extrusion surface 156A of the member 156 is disposed so as to be substantially separated from the extrusion surface 156A. Is arranged.
- the press-molding die body 152 is composed of a disk-shaped member having one end surface constituting a circular press-molding surface 152A.
- the shape of the press mold main body 152 is a disc shape in the example shown in FIG. 20, but the shape is not particularly limited as long as it is substantially a disc shape.
- the press molding surface 152A is a substantially flat surface.
- the support member 170 is fixedly disposed on one of the extruded surface 152B and the extruded surface 156A, and can be separated from the other surface. As the support member 170, for example, a ring-shaped member can be used.
- the guide member 154 can be pushed out by the first push member 156 to the other press mold side opposed to the press mold 200.
- the press mold body 152 is also pushed out to the other press mold side disposed opposite to the press mold 200 via the support member 170. Further, only the press mold main body 152 can be pushed out to the other press mold side facing the press mold 200 by the second pushing member 158.
- the press mold main body 152 is subjected to a pressing force in the vicinity of (1) the central portion of the extruded surface 152B or (2) the vicinity of the outer edge portion. For this reason, the thickness, material, strength, etc.
- the press mold main body 152 are set so that the press mold main body 152 does not bend even if a pressing force is applied to any position shown in the above (1) and (2). It is preferable to select a pressing condition such as a strength of the supporting member 170 or a pressing pressure.
- FIGS. 14 to 19 show the second press process.
- the press mold 150S shown in FIG. 20 or the press mold 200 shown in FIG. 21 may be used.
- the other press-molding die for example, a press-molding die which will be described later (for example, shown in FIG. A press mold 310) can be used.
- a part (for example, a press molding surface) of the other press mold comes into contact with the guide surface 154A, and in the second step, a part of the other press mold and the guide surface.
- the press mold main body 152 is further pushed out to the other press mold side in a state where it contacts with 154A.
- a glass material used in the method for producing a glass blank of the second embodiment it has physical properties suitable as a magnetic recording medium glass substrate, in particular, a high thermal expansion coefficient, further high rigidity, or heat resistance, and There is no particular limitation as long as it can be easily formed into a plate shape by horizontal direct pressing.
- the thermal expansion coefficient is desirably close to the thermal expansion coefficient of the holder that holds the magnetic recording medium.
- the average linear expansion coefficient at 100 to 300 ° C. is preferably 70 ⁇ 10 ⁇ 7 / ° C. or more, more preferably 75 ⁇ 10 ⁇ 7 / ° C. or more, and 80 ⁇ 10 ⁇ 7 / ° C.
- the temperature is not lower than ° C., and it is still more preferable that the temperature is 85 ⁇ 10 ⁇ 7 / ° C. or higher.
- the upper limit value of the average linear expansion coefficient is not particularly limited, but is practically preferably 120 ⁇ 10 ⁇ 7 / ° C. or less.
- a glass material having high rigidity is desired from the viewpoint of reducing the deflection generated during high-speed rotation of the magnetic recording medium.
- the Young's modulus is preferably 70 GPa or more, more preferably 75 GPa or more, and 80 GPa. More preferably, it is more preferably 85 GPa or more.
- the upper limit of the Young's modulus is not particularly limited, but is practically preferably 120 GPa or less.
- the glass transition temperature of the glass material is preferably 600 ° C. or higher, and 610 ° C. The above is more preferable, 620 ° C. or higher is further preferable, and 630 ° C. or higher is more preferable.
- the upper limit of the glass transition temperature is not particularly limited, but is preferably 780 ° C. or lower from a practical viewpoint such as suppressing the temperature during press molding from becoming high. Use of a glass material having a high thermal expansion coefficient, high rigidity, and heat resistance is effective in obtaining a glass substrate suitable for a magnetic recording medium having a high recording density.
- composition of the glass material a composition that can easily realize physical properties suitable as a magnetic recording medium glass substrate can be selected as appropriate.
- the glass composition of a glass material for conventional vertical direct press can be selected as appropriate, but an aluminosilicate glass Is preferably selected.
- aluminosilicate glass since it is easy to balance heat resistance, high rigidity, and a high thermal expansion coefficient in a well-balanced manner, the composition shown below is particularly preferable.
- the glass composition of this glass (hereinafter referred to as glass composition 1) is In mol% display, 50% to 75% of SiO 2 Al 2 O 3 from 0% to 5%, Li 2 O from 0% to 3%, ZnO from 0% to 5%, A total of 3-15% of at least one component selected from Na 2 O and K 2 O, A total of 14% to 35% of at least one component selected from MgO, CaO, SrO and BaO, and 2 to 9% in total of at least one component selected from ZrO 2 , TiO 2 , La 2 O 3 , Y 2 O 3 , Yb 2 O 3 , Ta 2 O 5 , Nb 2 O 5 and HfO 2 ; Including, The molar ratio ⁇ (MgO + CaO) / (MgO + CaO + SrO + BaO) ⁇ is in the range of 0.8 to 1, and the molar ratio ⁇ Al 2 O 3 / (MgO + CaO) ⁇ is in the range of
- a preferable range of the average linear expansion coefficient at 100 to 300 ° C. of glass composition 1 is 70 ⁇ 10 ⁇ 7 / ° C. or more, a preferable range of glass transition temperature is 630 ° C. or more, and a preferable range of Young's modulus is 80 GPa or more.
- Glass composition 1 is suitable as a material for an energy-assisted magnetic recording medium glass substrate using a high Ku magnetic material.
- glass composition 2 As a glass material having a high thermal expansion coefficient, excellent acid resistance and alkali resistance, little alkali elution from the substrate surface, and suitable for chemical strengthening, the following glass composition (referred to as glass composition 2) is used. Can show.
- the glass composition 2 is In mol% display, SiO 2 and Al 2 O 3 in total 70% to 85% (however, the content of SiO 2 is 50% or more, the content of Al 2 O 3 is 3% or more), Li 2 O, Na 2 O and K 2 O in total 10% or more, 1% to 6% in total of MgO and CaO (however, the content of CaO is larger than the content of MgO), ZrO 2 , TiO 2 , La 2 O 3 , Y 2 O 3 , Yb 2 O 3 , Ta 2 O 5 , Nb 2 O 5 and HfO 2 in total exceeding 0% and 4% or less, It is a composition containing.
- the magnetic recording medium glass substrate manufacturing method of the second embodiment is a magnetic recording medium that has undergone at least a polishing process for polishing the main surface of the glass blank produced by the glass blank manufacturing method of the second embodiment.
- a glass substrate is manufactured. Specific examples of the respective steps when processing a glass blank to form a magnetic recording medium glass substrate will be described in more detail below.
- Scribe is a glass blank that is cut into two concentric circles (inner concentric circle and outer concentric circle) by a scriber made of super steel alloy or diamond particles 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 difference in the thermal expansion of the glass removes the outer portion of the outer concentric circle and the inner portion of the inner concentric circle. As a result, a perfect circular disk-shaped glass is obtained.
- a cutting line can be suitably provided using a scriber.
- a scriber may not follow surface unevenness
- 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 the inner peripheral end of the ring-shaped glass with a diamond grindstone.
- the end face of the disk-shaped glass is polished.
- the inner peripheral side end surface and the outer peripheral side end surface of the glass are mirror-finished by brush polishing.
- 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 dust attached to the end surface of glass, damage or scratches by performing end face polishing Can do.
- first polishing is performed on the main surface of the 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 ⁇ m to 10 ⁇ m. 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.
- 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.
- 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.
- a plurality of disk-shaped glasses are held in each polishing carrier.
- 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 And the main surfaces of the front and back surfaces of the disk-shaped glass are polished.
- a hard resin polisher is used as the polishing pad, and for example, cerium oxide abrasive grains are used as the abrasive.
- the disc-shaped glass after the first polishing is chemically strengthened.
- a molten salt of potassium nitrate can be used as the chemical strengthening solution.
- the chemical strengthening solution 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 solution, for example, 3 hours to 4 hours. Soaked.
- the immersion is preferably performed in a state of being accommodated in a holder so that a plurality of glasses are held at the end faces so that both the main surfaces of the glass are chemically strengthened.
- the glass is strengthened and has good impact resistance.
- the chemically strengthened glass is washed. For example, after washing with sulfuric acid, it is washed with pure water, IPA (isopropyl alcohol) or the like.
- second polishing is performed on the glass that has been chemically strengthened and thoroughly cleaned.
- the machining allowance by the second polishing is, for example, about 1 ⁇ m.
- the second polishing is intended to finish the main surface in a mirror shape.
- 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.
- 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.
- a soft foamed resin polisher is used as the polishing pad, and as the abrasive, for example, cerium oxide abrasive grains that are finer than the cerium oxide abrasive grains used in the first polishing process are used.
- the disc-shaped glass polished in the second polishing step is washed again.
- a neutral detergent, pure water, and IPA are used.
- a glass substrate for a magnetic disk having a main surface flatness of 4 ⁇ m or less and a main surface roughness of 0.2 nm or less is obtained.
- each layer such as a magnetic layer is formed on the glass substrate for magnetic disk to produce a magnetic disk.
- the chemical strengthening step is performed between the first polishing step and the second polishing step, but is not limited to this order.
- the chemical strengthening step can be appropriately arranged.
- the order of the first polishing process, the second polishing process, and the chemical strengthening process (hereinafter, process order 1) may be used.
- the process order 1 since the surface unevenness
- the flatness of the glass blank used for processing and the flatness of the produced magnetic recording medium glass substrate can be made substantially the same.
- the flatness required for the magnetic recording medium glass substrate is recently required to be 10 ⁇ m or less (within 10 ⁇ m) for a 2.5-inch glass substrate, for example. This is because it can be easily achieved by the glass blank produced by the glass blank production method of the present embodiment.
- “the flatness of the glass blank used for processing and the flatness of the produced magnetic recording medium glass substrate are substantially the same” refers to the required flatness of the magnetic recording medium glass substrate ( 100%) means that the flatness of the glass blank is 105% or less.
- the magnetic recording medium manufacturing method of the second embodiment is a magnetic recording layer in which a magnetic recording layer is formed on a magnetic recording medium glass substrate manufactured by the magnetic recording medium glass substrate manufacturing method of the second embodiment.
- a magnetic recording medium is manufactured through at least a forming step.
- Magnetic recording media are called magnetic disks, hard disks, etc., internal storage devices (such as fixed disks) such as desktop computers, server computers, notebook computers, and mobile computers, and portable recording and playback that records and plays back images and / or audio. It is suitable for an internal storage device of a device, an in-vehicle audio recording / reproducing device, and the like.
- an adhesion layer, an underlayer, a magnetic layer (magnetic recording layer), a protective layer, and a lubricating layer are stacked on the main surface of a magnetic recording medium glass substrate in order from the side closer to the main surface.
- a magnetic recording medium glass substrate is introduced into a depressurized film forming apparatus, and an adhesion layer to a magnetic layer are sequentially formed on the main surface of the magnetic recording medium glass substrate in an Ar atmosphere by a DC magnetron sputtering method.
- CrTi can be used as the adhesion layer
- CrRu can be used as the underlayer.
- a magnetic recording medium can be formed by forming a protective layer using C 2 H 4 gas, for example, by the CVD method, and performing nitriding treatment for introducing nitrogen into the surface in the same chamber. it can. Thereafter, for example, PFPE (polyfluoropolyether) is applied on the protective layer by a dip coating method, whereby the lubricating layer can be formed.
- PFPE polyfluoropolyether
- the size of the magnetic recording medium is not particularly limited, but since the magnetic recording medium glass substrate is made of a glass material with excellent impact resistance, it is convenient to carry and may be exposed to external impacts. A size of 2.5 inches or less is preferred.
- a molten glass lump is disposed oppositely and substantially.
- the glass blank for a magnetic recording medium glass substrate (hereinafter referred to as “glass blank”) including a molding step of molding a sheet glass by direct pressing using a pair of press molds having the same temperature.
- the molten glass lump is pressed into a pair of presses until the temperature of the molten glass lump is equal to or lower than the temperature obtained by adding 10 ° C. to the strain point of the glass material constituting the sheet glass. It is characterized by continuing to press with a mold.
- the glass blank having a desired shape can be produced by preventing the deformation by continuing to press the molten glass lump with a pair of press-molding dies until the temperature is below the above temperature. In this case, it is preferable to continue to push the molten glass lump with a pair of press molds until the glass transition temperature of the glass material is reached.
- the glass blank cooling process can be controlled by maintaining the close contact state between the molten glass lump and the pair of press molds until the temperature falls below the strain point. It becomes possible to remove the distortion.
- the “adhered state” may be a state in which the molten glass lump is continuously pressed by a pair of press molds, and the pair of press molds does not apply force to the molten glass lump.
- adherence may be sufficient.
- the forming step includes a first pressing step for determining the plate thickness of the sheet glass and a second pressing step for improving the flatness of the sheet glass, the first pressing step,
- the second pressing step may be performed continuously using a pair of press molds. Furthermore, it is preferable to perform the forming step so that the plate-like glass has a thickness of 2 mm or less and a flatness of 10 ⁇ m or less (within 10 ⁇ m).
- the manufacturing method of the glass blank of 3rd this embodiment is suitable when manufacturing a thinner flat glass blank, it is more preferable to make plate
- the manufacturing method of the glass blank of 3rd this embodiment with each aspect of the manufacturing method of the glass blank of 1st this embodiment, or the manufacturing method of the glass blank of 1st this embodiment.
- the manufacturing method of the glass blank for magnetic recording medium glass substrates of 3rd this invention is each aspect of the manufacturing method of the glass blank of 2nd this embodiment, or the manufacturing method of the glass blank of 2nd this embodiment. You may combine.
- the manufacturing method of the magnetic recording medium glass substrate of the third embodiment is a method of manufacturing a glass blank by the manufacturing method of the glass blank of the third embodiment, and manufacturing the magnetic recording medium glass substrate by processing the glass blank. It is characterized by doing.
- other manufacturing conditions except for using a glass blank manufactured by the manufacturing method of the glass blank of the third embodiment It can be the same as the manufacturing method of the magnetic recording medium glass substrate of the first embodiment described above and / or the manufacturing method of the magnetic recording medium glass substrate of the second embodiment described above.
- a third method of manufacturing a magnetic recording medium according to the present embodiment is a method of manufacturing a magnetic recording medium glass substrate by the method of manufacturing a magnetic recording medium glass substrate of the third embodiment, and a magnetic recording layer on the magnetic recording medium glass substrate.
- a magnetic recording medium is manufactured through at least a magnetic recording layer forming step of forming a magnetic recording medium.
- the magnetic recording medium glass substrate manufactured by the method for manufacturing the magnetic recording medium glass substrate according to the third embodiment is used, except that the magnetic recording medium glass substrate is used.
- the manufacturing conditions can be the same as those of the magnetic recording medium manufacturing method of the first embodiment and / or the magnetic recording medium manufacturing method of the second embodiment described above.
- Example A1 A molten glass lump forming step, a first pressing step, a second pressing step, and a removing step were carried out by the processes shown in FIGS. 1 to 9 to produce a glass blank.
- the viscosity of the molten glass flowing out from the glass outlet 12 is adjusted to 700 dPa ⁇ s, and the first press mold 50 and the second press mold 60 are orthogonal to the dropping direction of the molten glass lump 24.
- the drop distance was set to 150 mm.
- the main physical property value and composition of the glass material used for preparation of the glass blank are as follows. Glass transition temperature: 495 ° C ⁇ Bend point: 550 °C ⁇ Strain point: 490 °C Composition: Composition corresponding to glass composition 2
- the temperature of the press molding surface 52A immediately before the first press process is 500 ° C.
- the temperature of the press molding surface 62A just before the first press process is 500 ° C.
- the surface of the press molding surface 52A just before the first press process is performed.
- the internal temperature difference was set to 50 ° C.
- the in-plane temperature difference of the press-molded surface 62A immediately before the first pressing step was set to 50 ° C.
- the press molds 50 and 60 were driven such that the press molding surface 52A and the press molding surface 62A were in contact with the molten glass lump 24 at the same time.
- the press molding time was 0.07 seconds.
- thermocouple disposed at a depth of 1 mm from the press molding surfaces 52A and 62A.
- This thermocouple is one at the center of the press molding surfaces 52A and 62A and one at a position of a radius of 30 mm from the center and at 0 °, 90 °, 180 ° and 270 ° in the circumferential direction. Has been placed.
- the duration of the second pressing process was set to 2 seconds.
- the temperature (extraction temperature) of the sheet glass 26 at the end of the second pressing step is 495 ° C.
- the pressing pressure during the second pressing step was set to always maintain 0.5 MPa.
- the temperature of the sheet glass 26 is a value obtained on the assumption that the temperature is measured by a thermocouple arranged at the center of the press molding surfaces 52A and 62A. In this way, the duration of the second pressing step was controlled using the flatness of the glass blank as an index to obtain a glass blank with excellent flatness.
- the press mold 50 was made of cast iron and used as an integral type in which a press mold main body 52 and a guide member 54 were integrally configured. Also, the press mold 60 was an integral type similar to the press mold 50.
- the press molding surfaces 52A and 62A are completely flat surfaces.
- cooling water is supplied into the press mold main bodies 52 and 62 so that the temperature of the press mold surfaces 52A and 62A and the in-plane temperature distribution can be controlled.
- a flow passage is provided, and a heater is disposed on the outer peripheral side of the press molds 50 and 60.
- the difference between the temperature of the press molding surface 52A of the press mold 50 and the temperature of the press molding surface 62A of the press mold 60 is always within ⁇ 10 ° C. Control was done to maintain range.
- Example A2 A glass blank was produced in the same manner as in Example A1, except that the duration of the second pressing step was further increased and the plate glass extraction temperature was set to 490 ° C.
- Example A3 A glass blank was used in the same manner as in Example A1, except that a separate mold type in which the press mold main bodies 52 and 62 and the guide members 54 and 64 were configured as separate members was used as the press molds 50 and 60. Produced.
- Example A4 A glass blank was produced in the same manner as in Example A3 except that the pressing pressure during the second pressing step was reduced with time.
- the press pressure was controlled to be 50% when the temperature of the sheet glass 26 reached the yield point of ⁇ 25 ° C., with the reference immediately after the start of the second press step (100%).
- Example A5 A glass blank was produced in the same manner as in Example A3 except that the pressing pressure during the second pressing step was reduced with time. Note that the press pressure was controlled to be 50% when the temperature of the sheet glass 26 reached the yield point + 25 ° C., with the reference immediately after the start of the second pressing step (100%).
- Example A6 A glass blank was produced in the same manner as in Example A3 except that the pressing pressure during the second pressing step was reduced with time. Note that the pressing pressure was controlled to be 50% when the temperature of the sheet glass 26 reached the yield point + 40 ° C., with the reference immediately after the start of the second pressing step (100%).
- Example A7 A glass blank was produced in the same manner as in Example A3 except that the pressing pressure during the second pressing step was reduced with time.
- the press pressure was controlled to be 50% when the temperature of the sheet glass 26 reached the yield point of ⁇ 40 ° C., with the reference immediately after the start of the second pressing step (100%).
- Example A8 A glass blank was produced in the same manner as in Example A3 except that the pressing pressure during the second pressing step was reduced with time. Note that the press pressure was controlled to be 50% when the temperature of the sheet glass 26 reached the yield point, with the reference immediately after the start of the second pressing step (100%).
- Example A9 A glass blank was produced in the same manner as in Example A2 except that the take-out temperature of the plate glass 26 was set to 485 ° C., and a separate type press mold was used as the press molds 50 and 60.
- Example A1 A glass blank was produced in the same manner as in Example A1 except that the duration of the second pressing step was set to less than 2 seconds and the plate glass extraction temperature was set to 520 ° C.
- Example A2 A glass blank was produced in the same manner as in Example A1, except that the second pressing step was omitted.
- Example A3 A glass blank was produced by vertical direct pressing using the same glass material as used in Example A1.
- twelve lower molds are arranged at equal intervals along the outer peripheral edge, and at the time of pressing, a rotary table that rotates while alternately repeating movement and stop every 30 degrees in one direction is provided.
- a press device was used.
- 12 lower mold stop positions corresponding to 12 lower molds arranged on the outer peripheral edge of the rotary table are numbered P1 to P12 along the rotation direction of the rotary table.
- the following members are respectively arranged on the lower die press surface or the lower die side at the following lower die stop position.
- Lower mold stop position P1 Molten glass supply device
- Lower mold stop position P2 Upper mold / Lower mold stop position
- P9 Extraction means (vacuum suction device)
- a predetermined amount of molten glass is supplied onto the lower mold at the lower mold stop position P1, and at the lower mold stop position P2, the molten glass is press-molded into a sheet glass by the upper mold and the lower mold. Then, plate glass (glass blank) is taken out at the lower mold stop position P9. Further, a soaking / cooling process is performed when the lower mold moves to the stop positions P2 to P9, and when the lower mold moves to the stop positions P9 to P12, the lower mold is preheated using a heater. .
- the material of the upper mold and the lower mold, and the smoothness and flatness of the press molding surface were the same as those of the press molds 50 and 60 used in Example A1.
- the viscosity of the molten glass immediately before being supplied onto the lower mold positioned at the lower mold stop position P1 was adjusted to 500 dPa ⁇ s.
- the details of the conditions for carrying out the pressing process are as follows.
- the temperature of the upper die press molding surface immediately before the pressing process is 380 ° C.
- the temperature of the lower die pressing surface immediately before the pressing step is 480 ° C.
- the in-plane temperature difference of the upper die pressing surface just before the pressing step is 30 ° C.
- the in-plane temperature difference of the lower die press-molding surface immediately before the pressing process was set to 30 ° C.
- the upper mold was driven downward two seconds after a predetermined amount of molten glass was supplied onto the lower mold. Further, the time (press molding time) from when the upper die contacts the molten glass on the lower die until the upper die and the lower die are separated from each other was set to 0.3 seconds.
- the temperature (extraction temperature) of the sheet glass at the end of the pressing process was 500 ° C.
- the temperature of the press molding surface of the upper mold and the lower mold was monitored by a thermocouple disposed at a position 5 mm deep from the press molding surface.
- One thermocouple is disposed at the center of the press molding surface and one thermocouple at a radius of 15 mm from the center and at 0 °, 90 °, 180 °, and 270 ° in the circumferential direction. Yes.
- Comparative Example A4 A glass blank was produced in the same manner as in Comparative Example A3, except that the press molding time was extended so that the extraction temperature was 495 ° C. In addition, since the production speed was very slow and there was no practicality, the press was stopped when several tens of glass blanks were produced.
- Comparative Example A5 As a pressing apparatus, an apparatus similar to the pressing apparatus used in Comparative Example A3 was used except that an upper mold for cooling was further arranged on the pressing surface at the lower mold stop position P3.
- the upper mold for cooling has substantially the same structure as the upper mold for press molding disposed on the press surface at the lower mold stop position P2.
- the pressing step performed at the lower mold stop position P2 was performed under the same conditions as in Comparative Example A3.
- the flatness was measured using a three-dimensional shape measuring device (manufactured by Coms Co., Ltd., high-precision three-dimensional shape measuring system, MAP-3D), and the average value of the flatness of ten samples was obtained.
- a three-dimensional shape measuring device manufactured by Coms Co., Ltd., high-precision three-dimensional shape measuring system, MAP-3D
- the number of glass blanks produced per unit time when 1000 glass blanks were produced continuously was determined.
- the evaluation criteria for the evaluation results shown in Tables 1 to 3 are as follows. A: The number of produced sheets per hour is 3420 or more B: The number of produced sheets per hour is 3240 or more and less than 3420 sheets C: The number of produced sheets per hour is 3060 or more and less than 3240 sheets D: The number of produced sheets per hour Less than 3060
- Example B1> Each glass blank produced in Examples A1 to A9 was annealed to reduce and remove strain. Next, scribing was performed on the outer peripheral portion and the central hole portion of the magnetic recording medium glass substrate. With such processing, two concentric grooves were formed on the outside and inside. Subsequently, the scribe-processed part was heated partially, the crack was generated along the scribe-processed groove
- the disk-shaped glass was subjected to shape processing by chamfering or the like, and further subjected to end face polishing.
- the glass was 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 recording medium glass substrate.
- the obtained magnetic recording medium glass substrate had an outer diameter of 65 mm, a center hole diameter of 20 mm, a thickness of 0.8 mm, and a main surface roughness of 0.2 nm or less.
- the flatness of the glass blanks of Examples A1 to A8 used for processing was 4 ⁇ m, and the flatness of the magnetic recording medium glass substrate prepared using the glass blanks of Examples A1 to A8 was 4 ⁇ m. There was almost no difference in the flatness of.
- the flatness of the glass blank of Example A9 used for processing was 3 ⁇ m, and the flatness of the magnetic recording medium glass substrate produced using the glass blank of Example A9 was 3 ⁇ m. There was little difference.
- the flatness of the magnetic recording medium glass substrate was measured in the same manner as the flatness of the glass blank.
- an adhesion layer, an underlayer, a magnetic layer, a protective layer, and a lubricating layer are formed in this order on the main surface of the magnetic recording medium glass substrate. Obtained.
- an adhesion layer, a base layer, and a magnetic layer were sequentially formed in an Ar atmosphere by a DC magnetron sputtering method using a vacuum-deposited film forming apparatus.
- the adhesion layer was formed using a CrTi target so as to be an amorphous CrTi layer having a thickness of 20 nm.
- a 10 nm thick layer made of amorphous CrRu was formed as a base layer by a DC magnetron sputtering method in an Ar atmosphere using a single wafer / stationary facing film forming apparatus.
- the magnetic layer was formed at a film forming temperature of 400 ° C. using an FePt or CoPt target so as to be an amorphous FePt or CoPt layer having a thickness of 200 nm.
- the magnetic recording medium after film formation up to the magnetic layer was transferred from the film forming apparatus to a heating furnace and annealed at a temperature of 650 to 700 ° C.
- a protective layer made of hydrogenated carbon was formed by a CVD method using ethylene as a material gas.
- a lubricating layer using PFPE perfluoropolyether
- the thickness of the lubricating layer was 1 nm.
- a magnetic recording medium was obtained by the above manufacturing process.
- the flatness of the magnetic recording media obtained using the glass blanks of Examples A1 to A8 was 4 ⁇ m, which was almost the same as the flatness of the magnetic recording medium glass substrate used for the production of the magnetic recording medium. Further, the flatness of the magnetic recording medium obtained using the glass blank of Example A9 was 3 ⁇ m, which was substantially the same as the flatness of the magnetic recording medium glass substrate used for producing the magnetic recording medium. The flatness of the magnetic recording medium was measured in the same manner as the flatness of the glass blank.
- a magnetic recording medium was produced in the same manner as in Example B1, using the obtained magnetic recording medium glass substrate.
- the flatness of the obtained magnetic recording medium was 4 ⁇ m, which was almost the same as the flatness of the magnetic recording medium glass substrate used for the production of the magnetic recording medium.
- a magnetic recording medium glass substrate and a magnetic recording medium were produced in the same manner as in Comparative Example B1, except that the glass blank produced in Comparative Example A5 was used.
- the obtained magnetic recording medium glass substrate had an outer diameter of 65 mm, a center hole diameter of 20 mm, a thickness of 0.8 mm, and a main surface roughness of 0.2 nm or less.
- the flatness of the glass blank used for processing was 15 ⁇ m, the flatness of the produced magnetic recording medium glass substrate was 4 ⁇ m, and it was confirmed that the flatness was greatly improved.
- a magnetic recording medium was produced in the same manner as in Comparative Example B1, using the obtained magnetic recording medium glass substrate.
- the flatness of the obtained magnetic recording medium was 4 ⁇ m, which was almost the same as the flatness of the magnetic recording medium glass substrate used for the production of the magnetic recording medium.
- Example A1 In the processes shown in FIGS. 11 to 19, a molten glass lump forming step, a press molding step (first step and second step), and an extraction step were carried out to produce a glass blank.
- the viscosity of the molten glass flowing out from the glass outlet 112 is adjusted to 700 dPa ⁇ s, and the first press mold 150 and the second press mold 160 are orthogonal to the dropping direction of the molten glass lump 124.
- the drop distance was set to 150 mm.
- the main physical property value and composition of the glass material used for preparation of the glass blank are as follows. Glass transition temperature: 495 ° C ⁇ Bend point: 550 °C ⁇ Strain point: 490 °C Composition: composition corresponding to the glass composition 2
- the temperature of the press molding surface 152A just before the first step is 500 ° C.
- the temperature of the press molding surface 162A just before the first step is 500 ° C.
- the in-plane temperature difference of the press molding surface 152A just before the first step is performed.
- the press molds 150 and 160 were driven so that the press molding surface 152A and the press molding surface 162A were in contact with the molten glass lump 124 at the same time.
- the press molding time was 0.07 seconds.
- thermocouple disposed at a depth of 30 mm from the press molding surfaces 152A and 162A.
- One thermocouple is provided at the center of the press molding surfaces 152A and 162A, and one at a position of a radius of 1 mm from the center and at 0 °, 90 °, 180 °, and 270 ° in the circumferential direction. Is arranged.
- the temperature (extraction temperature) of the sheet glass 126 at the end of the second step is set to be 495 ° C., and the press pressure of the press mold main bodies 152 and 162 during the second step is always 0.5 MPa. Set to maintain.
- the temperature of the sheet glass 126 is a value obtained on the assumption that the temperature is measured by a thermocouple arranged at the center of the press-molded surfaces 152A and 162A.
- the press mold 150 was made of cast iron and used as an integral type in which a press mold main body 152 and a guide member 154 were integrally formed.
- the press mold 160 was an integral type similar to the press mold 150.
- the press molding surfaces 152A and 162A are completely flat surfaces.
- the used press molds 150 and 160 have flow paths for flowing cooling water inside the press mold main bodies 152 and 162 so that the temperature of the press mold surfaces 152A and 162A and the in-plane temperature distribution can be controlled.
- a heater is disposed on the outer peripheral side of the press molds 150 and 160.
- Example A2 A glass blank was produced in the same manner as in Example A1, except that the extraction temperature was set to 490 ° C.
- Example A3 A glass blank was produced in the same manner as in Example A1, except that the extraction temperature was set to 505 ° C.
- Example A5 A glass blank was produced in the same manner as in Example A3, except that the pressing pressure during the second step was reduced with time. Note that the press pressure was controlled to be 50% when the temperature of the sheet glass 126 reached the yield point + 25 ° C., with the reference immediately after the start of the second step (100%).
- Example A6 A glass blank was produced in the same manner as in Example A3, except that the pressing pressure during the second step was reduced with time. Note that the press pressure was controlled to be 50% when the temperature of the sheet glass 126 reached the yield point of ⁇ 40 ° C., with the reference immediately after the start of the second step (100%).
- Example A7 A glass blank was produced in the same manner as in Example A3, except that the pressing pressure during the second step was reduced with time. Note that the press pressure was controlled to be 50% when the temperature of the sheet glass 126 reached the yield point + 40 ° C., with the reference immediately after the start of the second step (100%).
- Example A8 A glass blank was produced in the same manner as in Example A3, except that the pressing pressure during the second step was reduced with time. Note that the press pressure was controlled to be 50% when the temperature of the sheet glass 126 reached the yield point, with the reference immediately after the start of the second step (100%).
- Example A9 A glass blank was produced in the same manner as in Example A2 except that the extraction temperature was set to 485 ° C.
- Example A1 A glass blank was basically produced under the same conditions as in Example A1, except that the press mold 300 shown in FIG. 22 was used as the press mold. However, the press pressure was applied to the entire press mold 300 during the second step.
- the press mold 300 shown in FIG. 22 is made of cast iron and has a structure in which the press mold body 152 and the guide member 154 constituting the press mold 150S shown in FIG. 20 are integrated.
- the press mold 300 has a columnar shape, and one end surface is a press mold surface 300A.
- a ring-shaped convex portion 302 having a function similar to that of the guide member 154 is provided along the outer edge portion of the press molding surface.
- a rod-like member 304 is attached to the surface opposite to the press-molding surface 300A, and a drive device (not shown) is connected to the other end of the rod-like member 304.
- the rod-shaped member 304 is attached so as to be coaxial with the axial direction X of the press mold 300.
- the smoothness and flatness of the press molding surface 300A of the press mold 300, and the dimensions of each part of the press molding surface 300A and the convex portion 302 are substantially the same as the molding die 150S shown in FIG. 20 used in each example. The same as above.
- Example A2 A glass blank was basically produced under the same conditions as in Example A1, except that the press mold 310 shown in FIG. 23 was used as the press mold. However, the first step is finished when the thickness of the sheet glass 126 becomes approximately the same as the thickness of the glass blank to be produced, and then the second step is performed with the press pressure reduced. did. During the second step, the press pressure was applied to the entire press mold 310.
- the press mold 310 shown in FIG. 23 is made of cast iron and has a configuration corresponding to the press mold main body 152 constituting the press mold 150S shown in FIG.
- the press mold 310 is cylindrical, and one end surface is a press molding surface 310A. Further, a rod-like member 312 is attached to the surface opposite to the press-molding surface 310A, and a driving device (not shown) is connected to the other end of the rod-like member 312.
- the rod-shaped member 312 is attached so as to be coaxial with the axial direction X of the press mold 310.
- the flatness was measured using a three-dimensional shape measuring device (manufactured by Coms Co., Ltd., high-precision three-dimensional shape measuring system, MAP-3D), and the average value of the flatness of ten samples was obtained.
- a three-dimensional shape measuring device manufactured by Coms Co., Ltd., high-precision three-dimensional shape measuring system, MAP-3D
- -Thickness deviation The thickness deviation is measured with a micrometer at the center point of the produced glass blank and the positions at a radius of 30 mm and at 0 °, 90 °, 180 ° and 270 ° in the circumferential direction. Five standard deviations were determined. And the average value of the standard deviation of 10 samples was calculated
- Example B1> Each glass blank produced in Examples A1 to A9 was annealed to reduce and remove strain. Next, scribing was performed on the outer peripheral portion and the central hole portion of the magnetic recording medium glass substrate. With such processing, two concentric grooves were formed on the outside and inside. Subsequently, the scribe-processed part was heated partially, the crack was generated along the scribe-processed groove
- the disk-shaped glass was subjected to shape processing by chamfering or the like, and further subjected to end face polishing.
- the glass was 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 recording medium glass substrate.
- the obtained magnetic recording medium glass substrate had an outer diameter of 65 mm, a center hole diameter of 20 mm, a thickness of 0.8 mm, and a main surface roughness of 0.2 nm or less.
- the flatness of the glass blanks of Examples A1 to A8 used for processing was 4 ⁇ m, and the flatness of the magnetic recording medium glass substrate prepared using the glass blanks of Examples A1 to A8 was 4 ⁇ m. There was almost no difference in the flatness of.
- the flatness of the glass blank of Example A9 used for processing was 3 ⁇ m, and the flatness of the magnetic recording medium glass substrate produced using the glass blank of Example A9 was 3 ⁇ m. There was little difference.
- the flatness of the magnetic recording medium glass substrate was measured in the same manner as the flatness of the glass blank.
- an adhesion layer, an underlayer, a magnetic layer, a protective layer, and a lubricating layer are formed in this order on the main surface of the magnetic recording medium glass substrate. Obtained.
- an adhesion layer, a base layer, and a magnetic layer were sequentially formed in an Ar atmosphere by a DC magnetron sputtering method using a vacuum-deposited film forming apparatus.
- the adhesion layer was formed using a CrTi target so as to be an amorphous CrTi layer having a thickness of 20 nm.
- a 10 nm thick layer made of amorphous CrRu was formed as a base layer by a DC magnetron sputtering method in an Ar atmosphere using a single wafer / stationary facing film forming apparatus.
- the magnetic layer was formed at a film forming temperature of 400 ° C. using an FePt or CoPt target so as to be an amorphous FePt or CoPt layer having a thickness of 200 nm.
- the magnetic recording medium after film formation up to the magnetic layer was transferred from the film forming apparatus to a heating furnace and annealed at a temperature of 650 to 700 ° C.
- a protective layer made of hydrogenated carbon was formed by a CVD method using ethylene as a material gas.
- a lubricating layer using PFPE perfluoropolyether
- the thickness of the lubricating layer was 1 nm.
- a magnetic recording medium was obtained by the above manufacturing process.
- the flatness of the magnetic recording media obtained using the glass blanks of Examples A1 to A8 was 4 ⁇ m, which was almost the same as the flatness of the magnetic recording medium glass substrate used for the production of the magnetic recording medium. Further, the flatness of the magnetic recording medium obtained using the glass blank of Example A9 was 3 ⁇ m, which was substantially the same as the flatness of the magnetic recording medium glass substrate used for producing the magnetic recording medium. The flatness of the magnetic recording medium was measured in the same manner as the flatness of the glass blank.
- a magnetic recording medium glass substrate was produced using the glass blank produced in Comparative Example A1.
- magnetic recording was performed in the same manner as in Example B1, except that the lapping step was further performed by setting the grinding allowance to 50 ⁇ m after the end face polishing and before the first polishing.
- a medium glass substrate was produced.
- the obtained magnetic recording medium glass substrate had an outer diameter of 65 mm, a center hole diameter of 20 mm, a thickness of 0.8 mm, and a main surface roughness of 0.2 nm or less.
- the flatness of the glass blank used for processing was 15 ⁇ m, the flatness of the produced magnetic recording medium glass substrate was 4 ⁇ m, and it was confirmed that the flatness was greatly improved.
- a magnetic recording medium was produced in the same manner as in Example B1, using the obtained magnetic recording medium glass substrate.
- the flatness of the obtained magnetic recording medium was 4 ⁇ m, which was almost the same as the flatness of the magnetic recording medium glass substrate used for the production of the magnetic recording medium.
Landscapes
- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Manufacturing & Machinery (AREA)
- Materials Engineering (AREA)
- Organic Chemistry (AREA)
- Mechanical Engineering (AREA)
- Manufacturing Of Magnetic Record Carriers (AREA)
Abstract
Description
第一の本発明の磁気記録媒体ガラス基板用ガラスブランクの製造方法は、落下中の溶融ガラス塊を、当該溶融ガラス塊の落下方向に対して交差する方向に対向配置された第一のプレス成形型および第二のプレス成形型によりプレスし、板状に成形する第一のプレス工程と、第一のプレス成形型と第二のプレス成形型との間に形成された板状ガラスを、第一のプレス成形型と第二のプレス成形型とによりプレスし続ける第二のプレス工程と、該第二のプレス工程を経た後に、第一のプレス成形型と第二のプレス成形型とを離間して、第一のプレス成形型と第二のプレス成形型との間に挟持された板状ガラスを取り出す取出工程と、を少なくとも経て磁気記録媒体ガラス基板用ガラスブランクを製造し、少なくとも第一のプレス工程および第二のプレス工程の実施期間中において、第一のプレス成形型のプレス成形面の温度と、第二のプレス成形型のプレス成形面の温度とが、実質的に同一であり、第一のプレス工程において、第一のプレス成形型のプレス成形面と、第二のプレス成形型のプレス成形面とを、溶融ガラス塊に対して略同時に接触させた後に溶融ガラス塊をプレスすること、および、第二のプレス工程の継続時間を磁気記録媒体ガラス基板用ガラスブランクの平坦度が10μm以下(10μm以内)になるよう制御することを特徴とする。
第二の本発明の磁気記録媒体ガラス基板用ガラスブランクの製造方法は、落下中の溶融ガラス塊を、当該溶融ガラス塊の落下方向に対して交差する方向に対向配置された第一のプレス成形型および第二のプレス成形型によりプレス成形するプレス成形工程を、少なくとも経て、磁気記録媒体ガラス基板用ガラスブランクを製造し、少なくとも第一のプレス成形型が、プレス成形面を有するプレス成形型本体と、プレス成形時に、プレス成形面に対向配置された第二のプレス成形型側に押し出された際に、プレス成形面に対向配置された第二のプレス成形型の一部と接触することで、第一のプレス成形型および第二のプレス成形型のプレス成形面間の距離を略一定に保つ機能を少なくとも有するガイド部材と、を少なくとも備え、プレス成形工程が、第一のプレス成形型のガイド部材と、第二のプレス成形型と、が接触するまで、第一のプレス成形型および第二のプレス成形型を互いに接近させることで溶融ガラス塊を板状ガラスに成形する第一のステップと、第一のプレス成形型のガイド部材と、第二のプレス成形型とを接触させた状態で、第一のプレス成形型のプレス成形型本体と、第二のプレス成形型と、により板状ガラスをさらにプレスし続ける第二のステップと、を含むことを特徴とする。
(磁気記録媒体ガラス基板用ガラスブランクの製造方法)
第一の本実施形態の磁気記録媒体ガラス基板用ガラスブランクの製造方法(以下、「ガラスブランクの製造方法」と略す場合がある)は、落下中の溶融ガラス塊を、当該溶融ガラス塊の落下方向に対して交差する方向に対向配置された第一のプレス成形型および第二のプレス成形型によりプレスし、板状に成形する第一のプレス工程と、第一のプレス成形型と第二のプレス成形型との間に形成された板状ガラスを、第一のプレス成形型と第二のプレス成形型とによりプレスし続ける第二のプレス工程と、該第二のプレス工程を経た後に、第一のプレス成形型と第二のプレス成形型とを離間して、第一のプレス成形型と第二のプレス成形型との間に挟持された板状ガラスを取り出す取出工程と、を少なくとも経て磁気記録媒体ガラス基板用ガラスブランクを製造し、少なくとも第一のプレス工程および第二のプレス工程の実施期間中において、第一のプレス成形型のプレス成形面の温度と、第二のプレス成形型のプレス成形面の温度とが、実質的に同一であり、第一のプレス工程において、第一のプレス成形型のプレス成形面と、第二のプレス成形型のプレス成形面とを、溶融ガラス塊に対して略同時に接触させた後に溶融ガラス塊をプレスすること、および、
上記第二のプレス工程の継続時間を上記ガラスブランクの平坦度が10μm以下(10μm以内)になるよう制御することを特徴とする。ここで、本願明細書において、「磁気記録媒体ガラス基板」とは、非晶質ガラス(アモルファスガラス)製の磁気記録媒体用のガラス基板を意味する。
溶融ガラス塊形成工程では、プレス成形の対象物である溶融ガラス塊を作製する。溶融ガラス塊の作製方法としては特に限定されないが、通常は、溶融ガラスをガラス流出口から垂下させ、鉛直方向の下方側へと連続的に流出する溶融ガラス流の先端部を切断することで、溶融ガラス塊を形成する。なお、溶融ガラス流からその先端部を分離するように実施される切断には、一対のシアブレードを用いることができる。また、溶融ガラスの粘度としては先端部の切断や、プレス成形に適した粘度であれば特に限定されないが、通常は、500dPa・s~1050dPa・sの範囲内で、一定の値に制御されることが好ましい。
第一のプレス工程では、図3に示す落下中の溶融ガラス塊24を、溶融ガラス塊24の落下方向に対して交差する方向に対向配置された第一のプレス成形型および第二のプレス成形型によりプレスし、板状に成形する。ここで、第一のプレス成形型および第二のプレス成形型は、溶融ガラス塊24の落下方向に対して90度±1度の範囲内の角度を成すように略直交する方向に対向配置されていることが好ましく、溶融ガラス塊24の落下方向に対して直交する方向に対向配置されていることが特に好ましい。このように溶融ガラス塊24の落下方向に対して一対のプレス成形型を対向配置することにより、溶融ガラス塊24を両側から均等にプレスして板状に成形することがより容易となる。
第二のプレス工程では、第一のプレス成形型50と第二のプレス成形型60との間に形成された板状ガラス26を、第一のプレス成形型50と第二のプレス成形型60とによりプレスし続ける。すなわち、図7に示す第一のプレス工程が完了した直後の状態を維持しつつ、第一のプレス成形型50と第二のプレス成形型60とにより板状ガラス26をプレスし続ける。そして、この際、第二のプレス工程の継続時間を、ガラスブランクの平坦度が10μm以下(10μm以内)になるように制御する。
第二のプレス工程を経た後は、第一のプレス成形型50と第二のプレス成形型60とを離間して、第一のプレス成形型50と第二のプレス成形型60との間に挟持された板状ガラス26を取り出す取出工程を行う。この取出工程は、たとえば、以下に説明するように実施できる。まず、図8に示すように、第一のプレス成形型50と第二のプレス成形型60とを互いに離間させるように、第一のプレス成形型50を矢印X2方向へ移動させ、第二のプレス成形型60を矢印X1方向へ移動させる。これにより、プレス成形面62Aと、板状ガラス26とを離型させる。次いで、図9に示すように、プレス成形面52Aと、板状ガラス26とを離型させて、板状ガラス26を鉛直方向の下方Y1側に落下させて取り出す。なお、プレス成形面52Aと板状ガラス26とを離型させる際には、板状ガラス26の外周方向から力を加えて板状ガラス26を剥がすように離型することができる。この場合、板状ガラス26に大きな力を加えることなく、取出しを行うことができる。なお、取出しに際しては、プレス成形面52Aと板状ガラス26とを離型した後に、プレス成形面62Aと板状ガラス26とを離型してもよい。そして、最後に、取出した板状ガラス26を必要に応じてアニール処理して歪を低減・除去し、磁気記録媒体ガラス基板を加工するための母材、すなわち、ガラスブランクを得る。
以上に説明した第一の本実施形態のガラスブランクの製造方法により得られたガラスブランクは、その平坦度を10μm以下(10μm以内)とすることができ、4μm以下(4μm以内)とすることも極めて容易である。なお、ラッピング工程等の平坦性の改善を主たる目的として実施される後工程を省略または短縮する観点からは、平坦度は4μm以下(4μm以内)とすることが好ましい。
プレス成形型50、60を構成する材料としては、耐熱性、加工性、耐久性を考慮すると金属または合金が好ましい。この場合、溶融ガラスの温度を考慮すると、プレス成形型50、60を構成する金属または合金の耐熱温度は1000℃以上が好ましく、1100℃以上がより好ましい。プレス成形型50、60を構成する材料としては、具体的には、球状黒鉛鋳鉄(FCD)、合金工具鋼(SKD61など)、高速鋼(SKH)、超硬合金、コルモノイ、ステライトなどが好ましい。なお、プレス成形に際しては、水や空気などの冷却媒体を用いてプレス成形型50、60を冷却し、プレス成形型50、60の温度の上昇を抑制してもよい。また、プレス成形面52A、62Aの面内の温度分布を均一化するために、冷却媒体を利用してプレス成形面52A、62Aの中央部近傍を冷却したり、および/または、プレス成形型50、60の外周側にヒータ等の加熱部材を配置して、プレス成形面52A、62Aの外縁側を加熱してもよい。
第一の本実施形態のガラスブランクの製造方法に用いられるガラス材料としては、磁気記録媒体ガラス基板として好適な物性、特に、高熱膨張係数、さらに高剛性、あるいは耐熱性等を有し、かつ、水平ダイレクトプレスにより板状にプレス成形が容易なものであれば特に限定されない。熱膨張係数については、磁気記録媒体を保持する保持具の熱膨張係数に近いことが望まれる。具体的には、100~300℃における平均線膨張係数が70×10-7/℃以上であることが好ましく、75×10-7/℃以上であることがより好ましく、80×10-7/℃以上であることがさらに好ましく、85×10-7/℃以上であることが一層好ましい。平均線膨張係数の上限値は特に限定されるものではないが、実用上は、120×10-7/℃以下であることが好ましい。磁気記録媒体の高速回転時に生じるたわみを低減する上から高剛性のガラス材料が望まれるが、具体的には、ヤング率が70GPa以上であることが好ましく、75GPa以上であることがより好ましく、80GPa以上であることがさらに好ましく、85GPa以上であることが一層好ましい。ヤング率の上限値は特に限定されるものではないが、実用上は、120GPa以下であることが好ましい。さらに、耐熱性の優れたガラス材料を用いることにより、磁気記録媒体の製造過程で基板を高温で処理することが可能になることから、ガラス材料のガラス転移温度は600℃以上が好ましく、610℃以上がより好ましく、620℃以上がさらに好ましく、630℃以上が一層好ましい。なお、ガラス転移温度の上限値は特に限定されないが、プレス成形時の温度が高温となるのを抑制するなどの実用上の観点からは780℃以下であることが好ましい。高熱膨張係数、高剛性、耐熱性を兼備するガラス材料を使用することは、高記録密度の磁気記録媒体に好適なガラス基板を得る上から有効である。
モル%表示にて、
SiO2を50~75%、
Al2O3を0~5%、
Li2Oを0~3%、
ZnOを0~5%、
Na2OおよびK2Oから選択される少なくとも1種の成分を合計で3~15%、
MgO、CaO、SrOおよびBaOから選択される少なくとも1種の成分を合計で14~35%、ならびに、
ZrO2、TiO2、La2O3、Y2O3、Yb2O3、Ta2O5、Nb2O5およびHfO2から選択される少なくとも1種の成分を合計で2~9%、
含み、
モル比{(MgO+CaO)/(MgO+CaO+SrO+BaO)}が0.8~1の範囲であり、かつ、モル比{Al2O3/(MgO+CaO)}が0~0.30の範囲である。
モル%表示にて、
SiO2とAl2O3を合計で70~85%、ただし、SiO2の含有量が50%以上、Al2O3の含有量が3%以上、
Li2O、Na2OおよびK2Oを合計で10%以上、
MgOとCaOを合計で1~6%、ただし、CaOの含有量がMgOの含有量よりも多い、
ZrO2、TiO2、La2O3、Y2O3、Yb2O3、Ta2O5、Nb2O5およびHfO2を合計で0%を超えて4%以下、
含む組成である。
第一の本実施形態の磁気記録媒体ガラス基板の製造方法は、第一の本実施形態のガラスブランクの製造方法により作製されたガラスブランクの主表面を研磨する研磨工程を少なくとも経て、磁気記録媒体ガラス基板を製造することを特徴とする。以下にガラスブランクを加工して磁気記録媒体ガラス基板とする際の各工程の具体例についてより詳細に説明する。
第一の本実施形態の磁気記録媒体の製造方法は、第一の本実施形態の磁気記録媒体ガラス基板の製造方法により作製された磁気記録媒体ガラス基板上に磁気記録層を形成する磁気記録層形成工程を少なくとも経て、磁気記録媒体を製造することを特徴とする。
(磁気記録媒体ガラス基板用ガラスブランクの製造方法およびこれを用いた製造装置)
第二の本実施形態の磁気記録媒体ガラス基板用ガラスブランクの製造方法(以下、「ガラスブランクの製造方法」と略す場合がある。)は、落下中の溶融ガラス塊を、当該溶融ガラス塊の落下方向に対して交差する方向に対向配置された第一のプレス成形型および第二のプレス成形型によりプレス成形するプレス成形工程を、少なくとも経て、磁気記録媒体ガラス基板用ガラスブランク(以下、「ガラスブランク」と略す場合がある。)を製造する。
溶融ガラス塊形成工程では、プレス成形の対象物である溶融ガラス塊を作製する。溶融ガラス塊の作製方法としては特に限定されないが、通常は、溶融ガラスをガラス流出口から垂下させ、鉛直方向の下方側へと連続的に流出する溶融ガラス流の先端部を切断することで、溶融ガラス塊を形成する。なお、溶融ガラス流の先端部の切断には、一対のシアブレードを用いることができる。また、溶融ガラスの粘度としては先端部の切断や、プレス成形に適した粘度であれば特に限定されないが、通常は、500dPa・s~1050dPa・sの範囲内で、一定の値に制御されることが好ましい。なお、プレス成形直前の溶融ガラス塊の粘度も上記の範囲内とすることが好ましい。
第一のステップでは、図13に示す落下中の溶融ガラス塊124を、溶融ガラス塊124の落下方向に対して交差する方向に対向配置された第一のプレス成形型および第二のプレス成形型によりプレスし、板状に成形する。ここで、第一のプレス成形型および第二のプレス成形型は、溶融ガラス塊124の落下方向に対して90度±1度の角度を成すように略直交する方向に対向配置されていることが好ましく、溶融ガラス塊124の落下方向に対して直交する方向に対向配置されていることが特に好ましい。このように溶融ガラス塊124の落下方向に対して一対のプレス成形型を対向配置することにより、溶融ガラス塊124を両側から均等にプレスして板状に成形することがより容易となる。
第二のステップでは、図17に示すように第一のプレス成形型150のガイド部材154と第二のプレス成形型160のガイド部材164とを接触させた状態で、第一のプレス成形型150のプレス成形型本体152を矢印X1方向に移動させるように駆動させ、第二のプレス成形型160のプレス成形型本体162を矢印X2方向に移動させるように駆動させる。これにより、板状ガラス126を、プレス成形型本体152、162によりさらにプレスし続ける。
第二のステップを経た後は、第一のプレス成形型150と第二のプレス成形型160とを離間して、第一のプレス成形型150と第二のプレス成形型160との間に挟持された板状ガラス126を取り出す取出工程を行う。この取出工程は、たとえば、以下に説明するように実施できる。まず、図18に示すように、第一のプレス成形型150と第二のプレス成形型160とを互いに離間させるように、第一のプレス成形型150を矢印X2方向へ移動させ、第二のプレス成形型160を矢印X1方向へ移動させる。これにより、プレス成形面162Aと、板状ガラス126とを離型させる。次いで、図19に示すように、プレス成形面152Aと、板状ガラス126とを離型させて、板状ガラス126を鉛直方向の下方Y1側に落下させて取り出す。なお、プレス成形面152Aと板状ガラス126とを離型させる際には、板状ガラス126の外周方向から力を加えて板状ガラス126を剥がすように離型することができる。この場合、板状ガラス126に大きな力を加えることなく、取出しを行うことができる。なお、取出しに際しては、プレス成形面152Aと板状ガラス126とを離型した後に、プレス成形面162Aと板状ガラス126とを離型してもよい。そして、最後に、取出した板状ガラス126を必要に応じてアニール処理して歪を低減・除去し、磁気記録媒体ガラス基板を加工するための母材、すなわち、ガラスブランクを得る。
以上に説明した第二の本実施形態のガラスブランクの製造方法により得られたガラスブランクは、その平坦度を、たとえば、10μm以下(10μm以内)とすることができ、4μm以下(4μm以内)とすることも極めて容易である。なお、ラッピング工程等の平坦性の改善を主たる目的として実施される後工程を省略または短縮する観点からは、平坦度は4μm以下(4μm以内)とすることが好ましい。
第二の本実施形態のガラスブランクの製造方法に用いられるプレス成形型150は、プレス成形型本体152と、ガイド部材154とを少なくとも有する。そしてプレス成形型160も、プレス成形型本体162と、ガイド部材164とを少なくとも有し、プレス成形型150と同一の構造を有する。以下、プレス成形型150を例として説明する。まず、プレス成形型150は、プレス成形型本体152と、ガイド部材154とは別部材として構成されている。このため、第一のステップにおいては、プレス成形型本体152およびガイド部材154を一体的に、対向配置されたプレス成形型160側に押し出すように駆動させることができると共に、第二のステップにおいては、ガイド部材154に対してプレス成形型本体152のみを対向配置されたプレス成形型160側に相対的に押し出すように駆動させることが可能である。そして、プレス成形型150は、上述したような構造および機能を有するために、ガラスブランクの板厚偏差および平坦度をより小さくすることができる。
第二の本実施形態のガラスブランクの製造方法に用いられるガラス材料としては、磁気記録媒体ガラス基板として好適な物性、特に、高熱膨張係数、さらに高剛性、あるいは耐熱性等を有し、かつ、水平ダイレクトプレスにより板状にプレス成形が容易なものであれば特に限定されない。熱膨張係数については、磁気記録媒体を保持する保持具の熱膨張係数に近いことが望まれる。具体的には、100~300℃における平均線膨張係数が70×10-7/℃以上であることが好ましく、75×10-7/℃以上であることがより好ましく、80×10-7/℃以上であることがさらに好ましく、85×10-7/℃以上であることが一層好ましい。平均線膨張係数の上限値は特に限定されるものではないが、実用上は、120×10-7/℃以下であることが好ましい。磁気記録媒体の高速回転時に生じるたわみを低減する上から高剛性のガラス材料が望まれるが、具体的には、ヤング率が70GPa以上であることが好ましく、75GPa以上であることがより好ましく、80GPa以上であることがさらに好ましく、85GPa以上であることが一層好ましい。ヤング率の上限値は特に限定されるものではないが、実用上は、120GPa以下であることが好ましい。さらに、耐熱性の優れたガラス材料を用いることにより、磁気記録媒体の製造過程で基板を高温で処理することが可能になることから、ガラス材料のガラス転移温度は600℃以上が好ましく、610℃以上がより好ましく、620℃以上がさらに好ましく、630℃以上が一層好ましい。なお、ガラス転移温度の上限値は特に限定されないが、プレス成形時の温度が高温となるのを抑制するなどの実用上の観点からは780℃以下であることが好ましい。高熱膨張係数、高剛性、耐熱性を兼備するガラス材料を使用することは、高記録密度の磁気記録媒体に好適なガラス基板を得る上から有効である。
モル%表示にて、
SiO2を50%~75%、
Al2O3を0%~5%、
Li2Oを0%~3%、
ZnOを0%~5%、
Na2OおよびK2Oから選択される少なくとも1種の成分を合計で3%~15%、
MgO、CaO、SrOおよびBaOから選択される少なくとも1種の成分を合計で14%~35%、ならびに、
ZrO2、TiO2、La2O3、Y2O3、Yb2O3、Ta2O5、Nb2O5およびHfO2から選択される少なくとも1種の成分を合計で2~9%、
含み、さらに、
モル比{(MgO+CaO)/(MgO+CaO+SrO+BaO)}が0.8~1の範囲であり、かつ、モル比{Al2O3/(MgO+CaO)}が0~0.30の範囲である。
モル%表示にて、
SiO2とAl2O3を合計で70%~85%(ただし、SiO2の含有量が50%以上、Al2O3の含有量が3%以上)、
Li2O、Na2OおよびK2Oを合計で10%以上、
MgOとCaOを合計で1%~6%(ただし、CaOの含有量がMgOの含有量よりも多い)、
ZrO2、TiO2、La2O3、Y2O3、Yb2O3、Ta2O5、Nb2O5およびHfO2を合計で0%を超えて4%以下、
含む組成である。
第二の本実施形態の磁気記録媒体ガラス基板の製造方法は、第二の本実施形態のガラスブランクの製造方法により作製されたガラスブランクの主表面を研磨する研磨工程を少なくとも経て、磁気記録媒体ガラス基板を製造することを特徴とする。以下にガラスブランクを加工して磁気記録媒体ガラス基板とする際の各工程の具体例についてより詳細に説明する。
第二の本実施形態の磁気記録媒体の製造方法は、第二の本実施形態の磁気記録媒体ガラス基板の製造方法により作製された磁気記録媒体ガラス基板上に磁気記録層を形成する磁気記録層形成工程を少なくとも経て、磁気記録媒体を製造することを特徴とする。
(磁気記録媒体ガラス基板用ガラスブランクの製造方法)
第三の本実施形態の磁気記録媒体ガラス基板用ガラスブランクの製造方法(以下、「ガラスブランクの製造方法」と略す場合がある。)は、溶融ガラス塊を、対向配置され、かつ、実質的に同一温度である一対のプレス成形型を用いてダイレクトプレスすることにより、板状ガラスを成形する成形工程を含む磁気記録媒体ガラス基板用ガラスブランク(以下、「ガラスブランク」と略す場合がある。)の製造方法であって、成形工程においては、溶融ガラス塊の温度が、板状ガラスを構成するガラス材料の歪点に10℃を加えた温度以下になるまで、溶融ガラス塊を一対のプレス成形型で押し続けることを特徴とする。
プレス成形後にアニール処理を行うことによってガラスブランク内部の歪を解消(開放)する場合、歪点より10℃高い温度以下になるまでプレスを継続するだけでは、ガラスブランクの内部に歪が残ってしまう恐れがある。しかし、温度が歪点以下になるまで、溶融ガラス塊と一対のプレス成形型とを密着させた密着させた状態を維持することによって、ガラスブランクの冷却過程をコントロールすることができ、ガラスブランク内部の歪を抜くことが可能となる。これにより、アニール処理しても平坦度が悪化しにくいガラスブランクを得ることができる。なお「密着させた状態」とは、一対のプレス成形型により溶融ガラス塊を押し続けている状態であってもよく、一対のプレス成形型が溶融ガラス塊に力を加えることなく溶融ガラス塊に対して密着を維持していている状態でもよい。
第三の本実施形態の磁気記録媒体ガラス基板の製造方法は、第三の本実施形態のガラスブランクの製造方法によりガラスブランクを作製し、ガラスブランクを加工しての磁気記録媒体ガラス基板を作製することを特徴とする。なお、第三の本実施形態の磁気記録媒体ガラス基板の製造方法では、第三の本実施形態のガラスブランクの製造方法により作製されたガラスブランクを用いる点を除けば、その他の製造条件は、既述した第一の本実施形態の磁気記録媒体ガラス基板の製造方法および/または第二の本実施形態の磁気記録媒体ガラス基板の製造方法と同様とすることができる。
第三の本実施形態の磁気記録媒体の製造方法は、第三の本実施形態の磁気記録媒体ガラス基板の製造方法により磁気記録媒体ガラス基板を作製し、磁気記録媒体ガラス基板上に磁気記録層を形成する磁気記録層形成工程を少なくとも経て、磁気記録媒体を作製することを特徴とする。なお、第三の本実施形態の磁気記録媒体の製造方法では、第三の本実施形態の磁気記録媒体ガラス基板の製造方法により作製された磁気記録媒体ガラス基板を用いる点を除けば、その他の製造条件は、既述した第一の本実施形態の磁気記録媒体の製造方法および/または第二の本実施形態の磁気記録媒体の製造方法と同様とすることができる。
以下に第一の本発明を実施例を挙げて説明するが、第一の本発明は以下の実施例にのみ限定されるものではない。
各実施例および比較例では、2.5インチサイズの磁気記録媒体ガラス基板作製用のガラスブランク(直径:約75mm、厚み:約0.9mm)を連続的に数百枚以上作製した。
図1~図9に示したプロセスにて、溶融ガラス塊形成工程、第一のプレス工程、第二のプレス工程および取出工程を実施し、ガラスブランクを作製した。なお、ガラス流出口12から流出する溶融ガラスの粘度は700dPa・sに調整し、第一のプレス成形型50および第二のプレス成形型60は、溶融ガラス塊24の落下方向に対して直交するように配置し、落下距離は150mmに設定した。
・ガラス転移温度:495℃
・屈伏点:550℃
・歪点:490℃
・組成:ガラス組成2に相当する組成
第一のプレス工程実施直前のプレス成形面52Aの温度を500℃、第一のプレス工程実施直前のプレス成形面62Aの温度を500℃、第一のプレス工程実施直前のプレス成形面52Aの面内温度差を50℃、第一のプレス工程実施直前のプレス成形面62Aの面内温度差を50℃に設定した。なお、プレス成形型50、60の駆動は、プレス成形面52Aおよびプレス成形面62Aが、溶融ガラス塊24に同時に接触するように設定した。また、プレス成形時間は0.07秒とした。なお、プレス成形面52A、62Aの温度は、プレス成形面52A、62Aから深さ1mmの位置に配置した熱電対によりモニターした。この熱電対は、プレス成形面52A、62Aの中心部に1個と、中心部から半径30mmの位置であってかつ周方向に0°、90°、180°、270°の位置に各々1個配置されている。
第二のプレス工程の継続時間を調整し、得られたガラスブランクの平坦度を測定したところ、第二のプレス工程の継続時間を2秒以上にすると、ガラスブランクの平坦度が4μmとなった。そこで、第二のプレス工程の継続時間を2秒に設定した。第二のプレス工程終了時の板状ガラス26の温度(取出温度)を495℃である。第二のプレス工程実施中のプレス圧力は常に0.5MPaを維持するように設定した。なお、板状ガラス26の温度は、プレス成形面52A、62Aの中心部に配置された熱電対により測定された温度であると仮定して求めた値である。このようにして、ガラスブランクの平坦度を指標として第二のプレス工程の継続時間を制御し、平坦性の優れたガラスブランクを得た。
プレス成形型50は、鋳鉄製で、プレス成形型本体52とガイド部材54とが一体的に構成された一体型タイプのものを用いた。また、プレス成形型60もプレス成形型50と同様の一体型タイプのものを用いた。なお、プレス成形面52A、62Aは、完全な平坦面からなる。また、使用した一体型タイプのプレス成形型50、60には、プレス成形面52A、62Aの温度および面内温度分布が制御できるように、プレス成形型本体52、62の内部に、冷却水を流す流路が設けられると共に、プレス成形型50、60の外周側にヒータが配置されている。ここで、冷却水の流量およびヒータの加熱条件については、常にプレス成形型50のプレス成形面52Aの温度と、プレス成形型60のプレス成形面62Aの温度との差が、±10℃以内の範囲を維持するように制御した。
第二のプレス工程の継続時間をさらに長くして、板状ガラスの取出温度を490℃に設定した以外は、実施例A1と同様にしてガラスブランクを作製した。
プレス成形型50、60として、プレス成形型本体52、62とガイド部材54、64とが別部材として構成された分離型タイプのものを用いた以外は、実施例A1と同様にしてガラスブランクを作製した。
第二のプレス工程実施中のプレス圧力を、経時的に減少させた以外は、実施例A3と同様にしてガラスブランクを作製した。なお、プレス圧力は、第二のプレス工程の開始直後を基準(100%)とした場合、板状ガラス26の温度が屈伏点-25℃に達した時点で50%となるように制御した。
第二のプレス工程実施中のプレス圧力を、経時的に減少させた以外は、実施例A3と同様にしてガラスブランクを作製した。なお、プレス圧力は、第二のプレス工程の開始直後を基準(100%)とした場合、板状ガラス26の温度が屈伏点+25℃に達した時点で50%となるように制御した。
第二のプレス工程実施中のプレス圧力を、経時的に減少させた以外は、実施例A3と同様にしてガラスブランクを作製した。なお、プレス圧力は、第二のプレス工程の開始直後を基準(100%)とした場合、板状ガラス26の温度が屈伏点+40℃に達した時点で50%となるように制御した。
第二のプレス工程実施中のプレス圧力を、経時的に減少させた以外は、実施例A3と同様にしてガラスブランクを作製した。なお、プレス圧力は、第二のプレス工程の開始直後を基準(100%)とした場合、板状ガラス26の温度が屈伏点-40℃に達した時点で50%となるように制御した。
第二のプレス工程実施中のプレス圧力を、経時的に減少させた以外は、実施例A3と同様にしてガラスブランクを作製した。なお、プレス圧力は、第二のプレス工程の開始直後を基準(100%)とした場合、板状ガラス26の温度が屈伏点に達した時点で50%となるように制御した。
板状ガラス26の取出温度を485℃に設定し、かつ、プレス成形型50、60として分離型タイプのプレス成形型を用いた以外は、実施例A2と同様にしてガラスブランクを作製した。
第二のプレス工程の継続時間を2秒未満として板状ガラスの取出温度を520℃に設定した以外は、実施例A1と同様にしてガラスブランクを作製した。
第二のプレス工程の実施を省略した以外は、実施例A1と同様にしてガラスブランクを作製した。
実施例A1で用いたものと同様のガラス材料を用いて、垂直ダイレクトプレスによりガラスブランクを作製した。ガラスブランクの作製には、外周縁に沿って等間隔に下型が12個配置され、プレスに際しては、一方向に30度毎に移動と停止とを交互に繰り返しながら回転する回転テーブルを備えたプレス装置を用いた。また、回転テーブルの外周縁上に配置された12個の下型に対応する12個の下型停止位置に対して、回転テーブルの回転方向に沿ってP1~P12の番号を付した際に、以下の下型停止位置の下型プレス面上または下型の側には、各々下記の部材が配置されている。
・下型停止位置P1:溶融ガラス供給装置
・下型停止位置P2:上型
・下型停止位置P9:取出手段(真空吸着装置)
なお、プレス工程の実施条件の詳細は以下の通りである。プレス工程実施直前の上型プレス成形面の温度を380℃、プレス工程実施直前の下型プレス成形面の温度を480℃、プレス工程実施直前の上型プレス成形面の面内温度差を30℃、プレス工程実施直前の下型プレス成形面の面内温度差を30℃に設定した。なお、上型は、下型上に所定量の溶融ガラスが供給されてから2秒後に、下方に駆動させた。また、上型が下型上の溶融ガラスに接触してから、上型と下型とが離間するまでの時間(プレス成形時間)は0.3秒とした。以上に説明した条件でプレス工程を実施した場合、プレス工程終了時の板状ガラスの温度(取出温度)は、500℃であった。なお、上型および下型のプレス成形面の温度は、プレス成形面から深さ5mmの位置に配置した熱電対によりモニターした。この熱電対は、プレス成形面の中心部に1個と、中心部から半径15mmの位置であってかつ周方向に0°、90°、180°、270°の位置に各々1個配置されている。
取出温度が495℃となるようにプレス成形時間を延長した以外は、比較例A3と同様にしてガラスブランクを作製した。なお、生産速度が非常に遅く、実用性が無いため、ガラスブランクを数十枚程度作製した時点で、プレスを中止した。
プレス装置として、下型停止位置P3のプレス面上に冷却用上型を更に配置した以外は、比較例A3で用いたプレス装置と同様の装置を用いた。なお、冷却用上型は、下型停止位置P2のプレス面上に配置されたプレス成形用の上型と、実質的に同一の構造を有するものである。ここで、下型停止位置P2において実施されるプレス工程は、比較例A3と同様の条件で実施した。
各実施例および比較例において作製したガラスブランクについて、平坦度、割れ、および、生産性について評価した。結果を表1~表3に示す。なお、水平ダイレクトプレスによりガラスブランクを作製した全ての実施例および比較例A1,A2における第一のプレス工程および第二のプレス工程実施中のプレス成形面間の温度は、最大でも550℃以下であり、垂直ダイレクトプレスによりガラスブランクを作製した比較例A3~A5におけるプレス工程実施中のプレス成形面間の温度は、450℃~500℃の範囲内であった。
平坦度は、三次元形状測定装置(コムス株式会社製、高精度3次元形状測定システム、MAP-3D)を用いて測定し、10枚サンプルの平坦度の平均値を求めた。
ガラスブランクを連続して1000枚作製した場合に、得られたガラスブランクが割れたものをカウントし、割れの発生率を求めた。なお、表1~表3に示す評価結果の評価基準は以下の通りである。
A:割れの発生率が0%
B:割れの発生率が、0%を超え1%以下
C:割れの発生率が、1%を超え2%以下
D:割れの発生率が、2%以上
ガラスブランクを連続して1000枚作製した場合における単位時間当たりのガラスブランク生産枚数を求めた。なお、表1~表3に示す評価結果の評価基準は以下の通りである。
A:1時間当たりの生産枚数が3420枚以上
B:1時間当たりの生産枚数が3240枚以上3420枚未満
C:1時間当たりの生産枚数が3060枚以上3240枚未満
D:1時間当たりの生産枚数が3060枚未満
<実施例B1>
実施例A1~A9において作製した各ガラスブランクをアニールし、歪を低減、除去した。次に、磁気記録媒体ガラス基板の外周となる部分と中心孔になる部分にスクライブ加工を施した。こうした加工で、外側および内側に2つの同心円状の溝を形成した。次いで、スクライブ加工した部分を部分的に加熱して、ガラスの熱膨張の差異により、スクライブ加工した溝に沿ってクラックを発生させ、外側同心円の外側部分と内側部分とを除去した。これにより、真円形状のディスク状ガラスを得た。
比較例A1において作製したガラスブランクを用いて、磁気記録媒体ガラス基板を作製した。なお、磁気記録媒体ガラス基板の作製に際しては、端面研磨後にかつ第一研磨の実施前に、研削代を50μmに設定してラッピング工程を更に実施した以外は、実施例B1と同様にして磁気記録媒体ガラス基板を作製した。得られた磁気記録媒体ガラス基板の外径は65mm、中心孔径は20mm、厚さは0.8mm、主表面の粗さは0.2nm以下であった。また、加工に用いたガラスブランクの平坦度は15μmであり、作製された磁気記録媒体ガラス基板の平坦度は4μmであり、平坦度が大きく改善されていることが確認された。
ラッピング工程を省略した以外は、比較例B1と同様にして磁気記録媒体ガラス基板および磁気記録媒体を作製した。得られた磁気記録媒体ガラス基板および磁気記録媒体の平坦度は、加工に用いたガラスブランクの平坦度と実質同一であった。
比較例A5において作製したガラスブランクを用いた以外は、比較例B1と同様にして、磁気記録媒体ガラス基板および磁気記録媒体を作製した。得られた磁気記録媒体ガラス基板の外径は65mm、中心孔径は20mm、厚さは0.8mm、主表面の粗さは0.2nm以下であった。また、加工に用いたガラスブランクの平坦度は15μmであり、作製された磁気記録媒体ガラス基板の平坦度は4μmであり、平坦度が大きく改善されていることが確認された。
ラッピング工程を省略した以外は、比較例B3と同様にして磁気記録媒体ガラス基板および磁気記録媒体を作製した。得られた磁気記録媒体ガラス基板および磁気記録媒体の平坦度は、加工に用いたガラスブランクの平坦度と実質同一であった。
以下に第二の本発明を実施例を挙げて説明するが、第二の本発明は以下の実施例にのみ限定されるものではない。
各実施例および比較例では、2.5インチサイズの磁気記録媒体ガラス基板作製用のガラスブランク(直径:約75mm、厚み:約0.9mm)を連続的に数百枚以上作製した。
図11~図19に示したプロセスにて、溶融ガラス塊形成工程、プレス成形工程(第一のステップおよび第二のステップ)、ならびに、取出工程を実施し、ガラスブランクを作製した。なお、ガラス流出口112から流出する溶融ガラスの粘度は700dPa・sに調整し、第一のプレス成形型150および第二のプレス成形型160は、溶融ガラス塊124の落下方向に対して直交するように配置し、落下距離は150mmに設定した。
・ガラス転移温度:495℃
・屈伏点:550℃
・歪点:490℃
・組成:前記ガラス組成2に相当する組成
第一のステップ実施直前のプレス成形面152Aの温度を500℃、第一のステップ実施直前のプレス成形面162Aの温度を500℃、第一のステップ実施直前のプレス成形面152Aの面内温度差を50℃、第一のステップ実施直前のプレス成形面162Aの面内温度差を50℃に設定した。なお、プレス成形型150、160の駆動は、プレス成形面152Aおよびプレス成形面162Aが、溶融ガラス塊124に同時に接触するように設定した。また、プレス成形時間は0.07秒とした。なお、プレス成形面152A、162Aの温度は、プレス成形面152A、162Aから深さ30mmの位置に配置した熱電対によりモニターした。この熱電対は、プレス成形面152A、162Aの中心部に1個と、中心部から半径1mmの位置であってかつ周方向に0°、90°、180°、270°の位置に各々1個配置されている。
第二のステップ終了時の板状ガラス126の温度(取出温度)を495℃となるように設定し、第二のステップ実施中のプレス成形型本体152、162のプレス圧力は常に0.5MPaを維持するように設定した。なお、板状ガラス126の温度は、プレス成形面152A、162Aの中心部に配置された熱電対により測定された温度であると仮定して求めた値である。
プレス成形型150は、鋳鉄製で、プレス成形型本体152とガイド部材154とが一体的に構成された一体型タイプのものを用いた。また、プレス成形型160もプレス成形型150と同様の一体型タイプのものを用いた。なお、プレス成形面152A、162Aは、完全な平坦面からなる。また、使用したプレス成形型150、160には、プレス成形面152A、162Aの温度および面内温度分布が制御できるように、プレス成形型本体152、162の内部に、冷却水を流す流路が設けられると共に、プレス成形型150、160の外周側にヒータが配置されている。
取出温度を490℃に設定した以外は、実施例A1と同様にしてガラスブランクを作製した。
取出温度を505℃に設定した以外は、実施例A1と同様にしてガラスブランクを作製した。
第二のステップ実施中のプレス圧力を、経時的に減少させた以外は、実施例A3と同様にしてガラスブランクを作製した。なお、プレス圧力は、第二のステップの開始直後を基準(100%)とした場合、板状ガラス126の温度が屈伏点-25℃に達した時点で50%となるように制御した。
第二のステップ実施中のプレス圧力を、経時的に減少させた以外は、実施例A3と同様にしてガラスブランクを作製した。なお、プレス圧力は、第二のステップの開始直後を基準(100%)とした場合、板状ガラス126の温度が屈伏点+25℃に達した時点で50%となるように制御した。
第二のステップ実施中のプレス圧力を、経時的に減少させた以外は、実施例A3と同様にしてガラスブランクを作製した。なお、プレス圧力は、第二のステップの開始直後を基準(100%)とした場合、板状ガラス126の温度が屈伏点-40℃に達した時点で50%となるように制御した。
第二のステップ実施中のプレス圧力を、経時的に減少させた以外は、実施例A3と同様にしてガラスブランクを作製した。なお、プレス圧力は、第二のステップの開始直後を基準(100%)とした場合、板状ガラス126の温度が屈伏点+40℃に達した時点で50%となるように制御した。
第二のステップ実施中のプレス圧力を、経時的に減少させた以外は、実施例A3と同様にしてガラスブランクを作製した。なお、プレス圧力は、第二のステップの開始直後を基準(100%)とした場合、板状ガラス126の温度が屈伏点に達した時点で50%となるように制御した。
(実施例A9)
取出温度を485℃に設定した以外は、実施例A2と同様にしてガラスブランクを作製した。
プレス成形型として、図22に示すプレス成形型300を用いた以外は、基本的には実施例A1と同様の条件でガラスブランクを作製した。ただし、第二のステップ実施中において、プレス圧力は、プレス成形型300全体に加えた。
プレス成形型として、図23に示すプレス成形型310を用いた以外は、基本的には実施例A1と同様の条件でガラスブランクを作製した。ただし、第一のステップは、板状ガラス126の厚みが、作製しようとするガラスブランクの厚みと同程度となった時点で終了し、その後は、プレス圧力を弱くして第二のステップを実施した。また、第二のステップ実施中において、プレス圧力は、プレス成形型310全体に加えた。
各実施例および比較例において作製したガラスブランクについて、平坦度、板厚偏差、および、割れについて評価した。結果を表4および表5に示す。なお、実施例および比較例における第一のステップおよび第二のステップ実施中の2つのプレス成形面の温度は、双方ともほぼ同一の温度を示し、また、最高でも505℃以下であった。
平坦度は、三次元形状測定装置(コムス株式会社製、高精度3次元形状測定システム、MAP-3D)を用いて測定し、10枚サンプルの平坦度の平均値を求めた。
板厚偏差は、作製されたガラスブランクの中心点と、半径30mmの位置であってかつ周方向に0°、90°、180°、270°の位置とにおける厚みをマイクロメータで測定し、これら5点の標準偏差を求めた。そして、10枚のサンプルの標準偏差の平均値を求めた。
ガラスブランクを連続して1000枚作製した場合に、得られたガラスブランクが割れたものをカウントし、割れの発生率を求めた。なお、表4および表5に示す評価結果の評価基準は以下の通りである。
A:割れの発生率が0%
B:割れの発生率が、0%を超え1%以下
C:割れの発生率が、1%を超え2%以下
D:割れの発生率が、3%以上
<実施例B1>
実施例A1~A9において作製した各ガラスブランクをアニールし、歪を低減、除去した。次に、磁気記録媒体ガラス基板の外周となる部分と中心孔になる部分にスクライブ加工を施した。こうした加工で、外側および内側に2つの同心円状の溝を形成した。次いで、スクライブ加工した部分を部分的に加熱して、ガラスの熱膨張の差異により、スクライブ加工した溝に沿ってクラックを発生させ、外側同心円の外側部分と内側部分とを除去した。これにより、真円形状のディスク状ガラスを得た。
比較例A1において作製したガラスブランクを用いて、磁気記録媒体ガラス基板を作製した。なお、磁気記録媒体ガラス基板の作製に際しては、端面研磨後にかつ第一研磨の実施前に、研削代を50μmに設定してラッピング工程を更に実施した以外は、実施例B1と同様にして磁気記録媒体ガラス基板を作製した。得られた磁気記録媒体ガラス基板の外径は65mm、中心孔径は20mm、厚さは0.8mm、主表面の粗さは0.2nm以下であった。また、加工に用いたガラスブランクの平坦度は15μmであり、作製された磁気記録媒体ガラス基板の平坦度は4μmであり、平坦度が大きく改善されていることが確認された。
ラッピング工程を省略した以外は、比較例B1と同様にして磁気記録媒体ガラス基板および磁気記録媒体を作製した。得られた磁気記録媒体ガラス基板および磁気記録媒体の平坦度は、加工に用いたガラスブランクの平坦度と実質同一であった。
12 ガラス流出口
20 溶融ガラス流
22 先端部
24 溶融ガラス塊
26 板状ガラス
30 下側ブレード(シアブレード)
32 本体部
34 刃部
34U (刃部の)上面
34B (刃部の)下面
40 上側ブレード(シアブレード)
42 本体部
44 刃部
44U (刃部の)上面
44B (刃部の)下面
50 第一のプレス成形型
50S プレス成形型
52 プレス成形型本体
52A プレス成形面
52B 被押出面
54 ガイド部材
54A ガイド面
54B 被押出面
56 第一の押出部材
56A 押出面
56B 押出面56Aと反対側の面
56H 貫通穴
58 第二の押出部材
60 第二のプレス成形型
62 プレス成形型本体
62A プレス成形面
64 ガイド部材
64A ガイド面
112 ガラス流出口
120 溶融ガラス流
122 先端部
124 溶融ガラス塊
126 板状ガラス
130 下側ブレード(シアブレード)
132 本体部
134 刃部
134U (刃部の)上面
134B (刃部の)下面
140 上側ブレード(シアブレード)
142 本体部
144 刃部
144U (刃部の)上面
144B (刃部の)下面
150 第一のプレス成形型
150S プレス成形型
152 プレス成形型本体
152A プレス成形面
152B 被押出面
154 ガイド部材
154A ガイド面
154B 被押出面
156 第一の押出部材
156A 押出面
156B 押出面156Aと反対側の面
156H 貫通穴
158 第二の押出部材
160 第二のプレス成形型
162 プレス成形型本体
162A プレス成形面
164 ガイド部材
164A ガイド面
170 支持部材
200 プレス成形型
Claims (45)
- 落下中の溶融ガラス塊を、当該溶融ガラス塊の落下方向に対して交差する方向に対向配置された第一のプレス成形型および第二のプレス成形型によりプレスし、板状に成形する第一のプレス工程と、
上記第一のプレス成形型と上記第二のプレス成形型との間に形成された板状ガラスを、
上記第一のプレス成形型と上記第二のプレス成形型とによりプレスし続ける第二のプレス工程と、
該第二のプレス工程を経た後に、上記第一のプレス成形型と上記第二のプレス成形型とを離間して、上記第一のプレス成形型と上記第二のプレス成形型との間に挟持された上記板状ガラスを取り出す取出工程と、
を少なくとも経て磁気記録媒体ガラス基板用ガラスブランクを製造し、
少なくとも上記第一のプレス工程および上記第二のプレス工程の実施期間中において、上記第一のプレス成形型のプレス成形面の温度と、上記第二のプレス成形型のプレス成形面の温度とが、実質的に同一であり、
上記第一のプレス工程において、上記第一のプレス成形型のプレス成形面と、上記第二のプレス成形型のプレス成形面とを、上記溶融ガラス塊に対して略同時に接触させた後に上記溶融ガラス塊をプレスすること、および、
上記第二のプレス工程の継続時間を上記磁気記録媒体ガラス基板用ガラスブランクの平坦度が10μm以下になるよう制御することを特徴とする磁気記録媒体ガラス基板用ガラスブランクの製造方法。 - 請求項1に記載の磁気記録媒体ガラス基板用ガラスブランクの製造方法において、
前記第二のプレス工程の継続時間を、前記第二のプレス工程の終了時における前記板状ガラスの温度が、少なくとも、前記板状ガラスを構成するガラス材料の歪点に10℃を加えた温度以下となるように選択することを特徴とする磁気記録媒体ガラス基板用ガラスブランクの製造方法。 - 請求項1または2に記載の磁気記録媒体ガラス基板用ガラスブランクの製造方法において、
溶融ガラスをガラス流出口から垂下させ、鉛直方向の下方側へと連続的に流出する溶融ガラス流の先端部を切断することで、前記溶融ガラス塊を形成する溶融ガラス塊形成工程を含むことを特徴とする磁気記録媒体ガラス基板用ガラスブランクの製造方法。 - 請求項3に記載の磁気記録媒体ガラス基板用ガラスブランクの製造方法において、
前記溶融ガラスの粘度が、500dPa・s~1050dPa・sの範囲内であることを特徴とする磁気記録媒体ガラス基板用ガラスブランクの製造方法。 - 請求項1~4のいずれか1つに記載の磁気記録媒体ガラス基板用ガラスブランクの製造方法において、
前記第一のプレス成形型および前記第二のプレス成形型が、前記溶融ガラス塊の落下方向に対して直交する方向に対向配置されていることを特徴とする磁気記録媒体ガラス基板用ガラスブランクの製造方法。 - 請求項1~5のいずれか1つに記載の磁気記録媒体ガラス基板用ガラスブランクの製造方法において、
前記第一のプレス工程を実施する直前における、前記第一のプレス成形型および前記第二のプレス成形型のプレス成形面の温度が、前記溶融ガラス塊を構成するガラス材料の歪点に10℃を加えた温度以下であることを特徴とする磁気記録媒体ガラス基板用ガラスブランクの製造方法。 - 請求項1~6のいずれか1つに記載の磁気記録媒体ガラス基板用ガラスブランクの製造方法において、
前記第二のプレス工程におけるプレス圧力を、経時的に減少させることを特徴とする磁気記録媒体ガラス基板用ガラスブランクの製造方法。 - 請求項7に記載の磁気記録媒体ガラス基板用ガラスブランクの製造方法において、
前記プレス圧力を、前記第一のプレス成形型と前記第二のプレス成形型との間に挟持される前記板状ガラスの温度が、当該板状ガラスを構成するガラス材料の屈伏点±30℃の範囲内にまで低下した時点で、減少させることを特徴とする磁気記録媒体ガラス基板用ガラスブランクの製造方法。 - 請求項1~8のいずれか1つに記載の磁気記録媒体ガラス基板用ガラスブランクの製造方法において、
前記第二のプレス工程の実施中において、前記板状ガラスの一方の面と前記第一のプレス成形型のプレス成形面とを常に隙間無く密着させると共に、前記板状ガラスの他方の面と前記第二のプレス成形型のプレス成形面とを常に隙間無く密着させることを特徴とする磁気記録媒体ガラス基板用ガラスブランクの製造方法。 - 請求項1~9のいずれか1つに記載の磁気記録媒体ガラス基板用ガラスブランクの製造方法において、
前記第二のプレス工程の継続時間を、前記磁気記録媒体ガラス基板用ガラスブランクの平坦度が4μm以下になるように制御することを特徴とする磁気記録媒体ガラス基板用ガラスブランクの製造方法。 - 請求項1~10のいずれか1つに記載の磁気記録媒体ガラス基板用ガラスブランクの製造方法において、
前記第一のプレス成形型および前記第二のプレス成形型のプレス成形面の少なくとも前記板状ガラスと接触する領域が、略平坦な面であることを特徴とする磁気記録媒体ガラス基板用ガラスブランクの製造方法。 - 落下中の溶融ガラス塊を、当該溶融ガラス塊の落下方向に対して交差する方向に対向配置された第一のプレス成形型および第二のプレス成形型によりプレスし、板状に成形する第一のプレス工程と、
上記第一のプレス成形型と上記第二のプレス成形型との間に形成された板状ガラスを、
上記第一のプレス成形型と上記第二のプレス成形型とによりプレスし続ける第二のプレス工程と、
該第二のプレス工程を経た後に、上記第一のプレス成形型と上記第二のプレス成形型とを離間して、上記第一のプレス成形型と上記第二のプレス成形型との間に挟持された上記板状ガラスを取り出す取出工程と、を少なくとも経て磁気記録媒体ガラス基板用ガラスブランクを製造した後、
上記磁気記録媒体ガラス基板用ガラスブランクの主表面を研磨する研磨工程を少なくとも経て、磁気記録媒体ガラス基板を製造し、
少なくとも上記第一のプレス工程および上記第二のプレス工程の実施期間中において、上記第一のプレス成形型のプレス成形面の温度と、上記第二のプレス成形型のプレス成形面の温度とが、実質的に同一であり、
上記第一のプレス工程において、上記第一のプレス成形型のプレス成形面と、上記第二のプレス成形型のプレス成形面とを、上記溶融ガラス塊に対して略同時に接触させた後に上記溶融ガラス塊をプレスすること、および、
上記第二のプレス工程の継続時間を上記磁気記録媒体ガラス基板用ガラスブランクの平坦度が10μm以下になるよう制御することを特徴とする磁気記録媒体ガラス基板の製造方法。 - 請求項12に記載の磁気記録媒体ガラス基板の製造方法において、
前記第二のプレス工程の継続時間を、前記第二のプレス工程の終了時における前記板状ガラスの温度が、少なくとも、前記板状ガラスを構成するガラス材料の歪点に10℃を加えた温度以下となるように選択することを特徴とする磁気記録媒体ガラス基板の製造方法。 - 請求項12または13に記載の磁気記録媒体ガラス基板の製造方法において、
前記磁気記録媒体ガラス基板用ガラスブランクの平坦度と、前記磁気記録媒体ガラス基板の平坦度とが実質同一であることを特徴とする磁気記録媒体ガラス基板の製造方法。 - 落下中の溶融ガラス塊を、当該溶融ガラス塊の落下方向に対して交差する方向に対向配置された第一のプレス成形型および第二のプレス成形型によりプレスし、板状に成形する第一のプレス工程と、
上記第一のプレス成形型と上記第二のプレス成形型との間に形成された板状ガラスを、
上記第一のプレス成形型と上記第二のプレス成形型とによりプレスし続ける第二のプレス工程と、
該第二のプレス工程を経た後に、上記第一のプレス成形型と上記第二のプレス成形型とを離間して、上記第一のプレス成形型と上記第二のプレス成形型との間に挟持された上記板状ガラスを取り出す取出工程と、を少なくとも経て磁気記録媒体ガラス基板用ガラスブランクを製造した後、
上記磁気記録媒体ガラス基板用ガラスブランクの主表面を研磨する研磨工程を少なくとも経て、磁気記録媒体ガラス基板を製造し、さらに、
上記磁気記録媒体ガラス基板上に磁気記録層を形成する磁気記録層形成工程を少なくとも経て、磁気記録媒体を製造し、
少なくとも上記第一のプレス工程および上記第二のプレス工程の実施期間中において、上記第一のプレス成形型のプレス成形面の温度と、上記第二のプレス成形型のプレス成形面の温度とが、実質的に同一であり、
上記第一のプレス工程において、上記第一のプレス成形型のプレス成形面と、上記第二のプレス成形型のプレス成形面とを、上記溶融ガラス塊に対して略同時に接触させた後に上記溶融ガラス塊をプレスすること、および、
上記第二のプレス工程の継続時間を上記磁気記録媒体ガラス基板用ガラスブランクの平坦度が10μm以下になるよう制御することを特徴とする磁気記録媒体の製造方法。 - 請求項15に記載の磁気記録媒体の製造方法において、
前記第二のプレス工程の継続時間を、前記第二のプレス工程の終了時における前記板状ガラスの温度が、少なくとも、前記板状ガラスを構成するガラス材料の歪点に10℃を加えた温度以下となるように選択することを特徴とする磁気記録媒体の製造方法。 - 請求項15または16に記載の磁気記録媒体の製造方法において、
前記磁気記録媒体ガラス基板用ガラスブランクの平坦度と、前記磁気記録媒体ガラス基板の平坦度とが実質同一であることを特徴とする磁気記録媒体の製造方法。 - 落下中の溶融ガラス塊を、当該溶融ガラス塊の落下方向に対して交差する方向に対向配置された第一のプレス成形型および第二のプレス成形型によりプレス成形するプレス成形工程を、少なくとも経て、磁気記録媒体ガラス基板用ガラスブランクを製造し、
少なくとも上記第一のプレス成形型が、
プレス成形面を有するプレス成形型本体と、
プレス成形時に、上記プレス成形面に対向配置された上記第二のプレス成形型側に押し出された際に、上記プレス成形面に対向配置された上記第二のプレス成形型の一部と接触することで、上記第一のプレス成形型および上記第二のプレス成形型のプレス成形面間の距離を略一定に保つ機能を少なくとも有するガイド部材と、を少なくとも備え、
上記プレス成形工程が、
上記第一のプレス成形型のガイド部材と、上記第二のプレス成形型と、が接触するまで、上記第一のプレス成形型および上記第二のプレス成形型を互いに接近させることで上記溶融ガラス塊を板状ガラスに成形する第一のステップと、
上記第一のプレス成形型のガイド部材と、上記第二のプレス成形型とを接触させた状態で、上記第一のプレス成形型のプレス成形型本体と、上記第二のプレス成形型と、により上記板状ガラスをさらにプレスし続ける第二のステップと、
を含むことを特徴とする磁気記録媒体ガラス基板用ガラスブランクの製造方法。 - 請求項18に記載の磁気記録媒体ガラス基板用ガラスブランクの製造方法において、
前記第一のプレス成形型および前記第二のプレス成形型の各々が、
プレス成形面を有するプレス成形型本体と、
プレス成形時に、上記プレス成形面に対向配置された他方のプレス成形型側に押し出された際に、上記プレス成形面に対向配置された他方のプレス成形型の一部と接触することで、前記第一のプレス成形型および前記第二のプレス成形型のプレス成形面間の距離を略一定に保つ機能を少なくとも有するガイド部材と、を少なくとも備え、
前記第一のステップが、
前記第一のプレス成形型のガイド部材と、前記第二のプレス成形型のガイド部材と、が接触するまで、前記第一のプレス成形型および前記第二のプレス成形型を互いに接近させることにより実施され、
前記第二のステップが、
前記第一のプレス成形型のガイド部材と、前記第二のプレス成形型のガイド部材とを接触させた状態で、前記第一のプレス成形型のプレス成形型本体と、前記第二のプレス成形型のプレス成形型本体と、により前記板状ガラスをさらにプレスし続けることにより実施されることを特徴とする磁気記録媒体ガラス基板用ガラスブランクの製造方法。 - 請求項18または19に記載の磁気記録媒体ガラス基板用ガラスブランクの製造方法において、
溶融ガラスをガラス流出口から垂下させ、鉛直方向の下方側へと連続的に流出する溶融ガラス流の先端部を切断することで、前記溶融ガラス塊を形成する溶融ガラス塊形成工程を含むことを特徴とする磁気記録媒体ガラス基板用ガラスブランクの製造方法。 - 請求項20に記載の磁気記録媒体ガラス基板用ガラスブランクの製造方法において、
前記溶融ガラスの粘度が、500dPa・s~1050dPa・sの範囲内であることを特徴とする磁気記録媒体ガラス基板用ガラスブランクの製造方法。 - 請求項18~21のいずれか1つに記載の磁気記録媒体ガラス基板用ガラスブランクの製造方法において、
前記第一のプレス成形型および前記第二のプレス成形型が、前記溶融ガラス塊の落下方向に対して直交する方向に対向配置されていることを特徴とする磁気記録媒体ガラス基板用ガラスブランクの製造方法。 - 請求項18~22のいずれか1つに記載の磁気記録媒体ガラス基板用ガラスブランクの製造方法において、
前記第二のステップの継続時間を前記磁気記録媒体ガラス基板用ガラスブランクの平坦度が10μm以下になるように制御することを特徴とする磁気記録媒体ガラス基板用ガラスブランクの製造方法。 - 請求項18~23のいずれか1つに記載の磁気記録媒体ガラス基板用ガラスブランクの製造方法において、
前記第二のステップの継続時間を、前記第二のステップの終了時における前記板状ガラスの温度が、少なくとも、前記板状ガラスを構成するガラス材料の歪点に10℃を加えた温度以下となるように選択することを特徴とする磁気記録媒体ガラス基板用ガラスブランクの製造方法。 - 請求項18~24のいずれか1つに記載の磁気記録媒体ガラス基板用ガラスブランクの製造方法において、
前記第一のステップを実施する直前における、前記第一のプレス成形型のプレス成形面の温度と、前記第二のプレス成形型のプレス成形面の温度と、の差の絶対値が0℃~10℃の範囲内であることを特徴とする磁気記録媒体ガラス基板用ガラスブランクの製造方法。 - 請求項18~25のいずれか1つに記載の磁気記録媒体ガラス基板用ガラスブランクの製造方法において、
前記第一のステップを実施する直前における、前記第一のプレス成形型および前記第二のプレス成形型のプレス成形面の面内温度差の絶対値が0℃~100℃の範囲内であることを特徴とする磁気記録媒体ガラス基板用ガラスブランクの製造方法。 - 請求項18~26のいずれか1つに記載の磁気記録媒体ガラス基板用ガラスブランクの製造方法において、
少なくとも前記プレス成形工程の実施期間中における、前記第一のプレス成形型のプレス成形面の温度と、前記第二のプレス成形型のプレス成形面の温度とが、実質的に同一であり、かつ、
前記第一のプレス成形型のプレス成形面と、前記第二のプレス成形型のプレス成形面とを、前記溶融ガラス塊に対して略同時に接触させた後に前記溶融ガラス塊をプレス成形することを特徴とする磁気記録媒体ガラス基板用ガラスブランクの製造方法。 - 請求項18~27のいずれか1つに記載の磁気記録媒体ガラス基板用ガラスブランクの製造方法において
前記板状ガラスの温度が、少なくとも前記板状ガラスを構成するガラス材料の歪点に10℃を加えた温度以下となるまで、前記第二のステップが継続されることを特徴とする磁気記録媒体ガラス基板用ガラスブランクの製造方法。 - 請求項18~28のいずれか1つに記載の磁気記録媒体ガラス基板用ガラスブランクの製造方法において、
前記第二のステップにおけるプレス圧力を、経時的に減少させることを特徴とする磁気記録媒体ガラス基板用ガラスブランクの製造方法。 - 請求項29に記載の磁気記録媒体ガラス基板用ガラスブランクの製造方法において、
前記プレス圧力を、前記第一のプレス成形型と前記第二のプレス成形型との間に挟持される前記板状ガラスの温度が、当該板状ガラスを構成するガラス材料の屈伏点±30℃の範囲内にまで低下した時点で、減少させることを特徴とする磁気記録媒体ガラス基板用ガラスブランクの製造方法。 - 請求項18~30のいずれか1つに記載の磁気記録媒体ガラス基板用ガラスブランクの製造方法において、
前記磁気記録媒体ガラス基板用ガラスブランクの平坦度が10μm以下であることを特徴とする磁気記録媒体ガラス基板用ガラスブランクの製造方法。 - 請求項18~31のいずれか1つに記載の磁気記録媒体ガラス基板用ガラスブランクの製造方法において、
前記磁気記録媒体ガラス基板用ガラスブランクの平坦度が4μm以下であることを特徴とする磁気記録媒体ガラス基板用ガラスブランクの製造方法。 - 請求項18~32のいずれか1つに記載の磁気記録媒体ガラス基板用ガラスブランクの製造方法において、
前記第一のプレス成形型および前記第二のプレス成形型のプレス成形面の少なくとも前記板状ガラスと接触する領域が、略平坦な面であることを特徴とする磁気記録媒体ガラス基板用ガラスブランクの製造方法。 - 請求項18~33のいずれか1つに記載の磁気記録媒体ガラス基板用ガラスブランクの製造方法において、
前記第一のプレス成形型および前記第二のプレス成形型の各々が、
前記プレス成形型本体と前記ガイド部材とを、前記プレス成形面と直交する方向であって、かつ、前記プレス成形面に対向配置された他方のプレス成形型側に、同時に押し出す第一の押出部材と、
該第一の押出部材によって、前記ガイド部材と前記プレス成形面に対向配置された他方のプレス成形型の一部とが接触した後に、前記プレス成形型本体を、前記プレス成形面と直交する方向であって、かつ、前記プレス成形面に対向配置された他方のプレス成形型側に押し出す第二の押出部材と、を更に備えることを特徴とする磁気記録媒体ガラス基板用ガラスブランクの製造方法。 - 落下中の溶融ガラス塊を、当該溶融ガラス塊の落下方向に対して交差する方向に対向配置された第一のプレス成形型および第二のプレス成形型によりプレス成形するプレス成形工程を、少なくとも経て、磁気記録媒体ガラス基板用ガラスブランクを製造した後、
上記磁気記録媒体ガラス基板用ガラスブランクの主表面を研磨する研磨工程を少なくとも経て磁気記録媒体ガラス基板を製造し、
少なくとも上記第一のプレス成形型が、
プレス成形面を有するプレス成形型本体と、
プレス成形時に、上記プレス成形面に対向配置された上記第二のプレス成形型側に押し出された際に、上記プレス成形面に対向配置された上記第二のプレス成形型の一部と接触することで、上記第一のプレス成形型および上記第二のプレス成形型のプレス成形面間の距離を略一定に保つ機能を少なくとも有するガイド部材と、を少なくとも備え、
上記プレス成形工程が、
上記第一のプレス成形型のガイド部材と、上記第二のプレス成形型と、が接触するまで、上記第一のプレス成形型および上記第二のプレス成形型を互いに接近させることで上記溶融ガラス塊を板状ガラスに成形する第一のステップと、
上記第一のプレス成形型のガイド部材と、上記第二のプレス成形型とを接触させた状態で、上記第一のプレス成形型のプレス成形型本体と、上記第二のプレス成形型と、により上記板状ガラスをさらにプレスし続ける第二のステップと、
を含むことを特徴とする磁気記録媒体ガラス基板の製造方法。 - 請求項35に記載の磁気記録媒体ガラス基板の製造方法において、
前記磁気記録媒体ガラス基板用ガラスブランクの平坦度と、前記磁気記録媒体ガラス基板の平坦度とが実質同一であることを特徴とする磁気記録媒体ガラス基板の製造方法。 - 落下中の溶融ガラス塊を、当該溶融ガラス塊の落下方向に対して交差する方向に対向配置された第一のプレス成形型および第二のプレス成形型によりプレス成形するプレス成形工程を、少なくとも経て、磁気記録媒体ガラス基板用ガラスブランクを製造した後、
上記磁気記録媒体ガラス基板用ガラスブランクの主表面を研磨する研磨工程を少なくとも経て磁気記録媒体ガラス基板を製造し、さらに、
上記磁気記録媒体ガラス基板上に磁気記録層を形成する磁気記録層形成工程を少なくとも経て、磁気記録媒体を製造し、
少なくとも上記第一のプレス成形型が、
プレス成形面を有するプレス成形型本体と、
プレス成形時に、上記プレス成形面に対向配置された上記第二のプレス成形型側に押し出された際に、上記プレス成形面に対向配置された上記第二のプレス成形型の一部と接触することで、上記第一のプレス成形型および上記第二のプレス成形型のプレス成形面間の距離を略一定に保つ機能を少なくとも有するガイド部材と、を少なくとも備え、
上記プレス成形工程が、
上記第一のプレス成形型のガイド部材と、上記第二のプレス成形型と、が接触するまで、上記第一のプレス成形型および上記第二のプレス成形型を互いに接近させることで上記溶融ガラス塊を板状ガラスに成形する第一のステップと、
上記第一のプレス成形型のガイド部材と、上記第二のプレス成形型とを接触させた状態で、上記第一のプレス成形型のプレス成形型本体と、上記第二のプレス成形型と、により上記板状ガラスをさらにプレスし続ける第二のステップと、
を含むことを特徴とする磁気記録媒体の製造方法。 - 請求項37に記載の磁気記録媒体の製造方法において、
前記磁気記録媒体ガラス基板用ガラスブランクの平坦度と、前記磁気記録媒体ガラス基板の平坦度とが実質同一であることを特徴とする磁気記録媒体の製造方法。 - 溶融ガラス流を鉛直方向下方側へと垂下する流出口を備えた溶融ガラス流出管と、
上記溶融ガラス流出管から流出する溶融ガラス流の垂下する方向に対して略直交する方向であって、上記溶融ガラス流の垂下する方向の両側に対向配置され、上記溶融ガラス流の両側から貫入させることにより上記溶融ガラス流の先端部を切断して溶融ガラス塊を形成する一対のシアブレードと、
鉛直方向下方側へと落下する上記溶融ガラス塊の落下する方向に対して略直交する方向であって、上記溶融ガラス塊の落下する方向の両側に対向配置され、上記溶融ガラス塊を両側から挟み込むことにより上記溶融ガラス塊を板状ガラスにプレス成形する第一のプレス成形型および第二のプレス成形型と、を少なくとも備え、
少なくとも上記第一のプレス成形型が、
プレス成形面を有するプレス成形型本体と、
プレス成形時に、上記プレス成形面に対向配置された上記第二のプレス成形型側に押し出された際に、上記プレス成形面に対向配置された上記第二のプレス成形型の一部と接触することで、上記第一のプレス成形型および上記第二のプレス成形型のプレス成形面間の距離を略一定に保つ機能を少なくとも有するガイド部材と、
上記プレス成形型本体と上記ガイド部材とを、上記プレス成形面と直交する方向であって、かつ、上記プレス成形面に対向配置された上記第二のプレス成形型側に、同時に押し出す第一の押出部材と、
該第一の押出部材によって、上記ガイド部材と上記プレス成形面に対向配置された上記第二のプレス成形型の一部とが接触した後に、上記プレス成形型本体を、上記プレス成形面と直交する方向であって、かつ、上記プレス成形面に対向配置された上記第二のプレス成形型側に押し出す第二の押出部材と、
を少なくとも備えることを特徴とする磁気記録媒体ガラス基板用ガラスブランクの製造装置。 - 溶融ガラス塊を、対向配置され、かつ、実質的に同一温度である一対のプレス成形型を用いてダイレクトプレスすることにより、板状ガラスを成形する成形工程を含む磁気記録媒体ガラス基板用ガラスブランクの製造方法であって、
前記成形工程においては、上記溶融ガラス塊の温度が、上記板状ガラスを構成するガラス材料の歪点に10℃を加えた温度以下になるまで、上記溶融ガラス塊を上記一対のプレス成形型で押し続けることを特徴とする磁気記録媒体ガラス基板用ガラスブランクの製造方法。 - 請求項40に記載の磁気記録媒体ガラス基板用ガラスブランクの製造方法において、
前記溶融ガラス塊の温度が前記ガラス材料の歪点以下になるまで、前記溶融ガラス塊と前記一対のプレス成形型とを密着させた状態を維持した後、アニール処理を行うことを特徴とする磁気記録媒体ガラス基板用ガラスブランクの製造方法。 - 請求項40または41に記載の磁気記録媒体ガラス基板用ガラスブランクの製造方法において、
前記成形工程は、前記板状ガラスの板厚を決定するための第一のプレス工程と、前記板状ガラスの平坦度を向上させるための第二のプレス工程とを含み、
前記第一のプレス工程と前記第二のプレス工程とは、前記一対のプレス成形型を用いて連続的に行われることを特徴とする磁気記録媒体ガラス基板用ガラスブランクの製造方法。 - 請求項40~42のいずれか1つに記載の磁気記録媒体ガラス基板用ガラスブランクの製造方法において、
前記板状ガラスの板厚が2mm以下であり、かつ、平坦度が10μm以下となるように、前記成形工程を実施することを特徴とする磁気記録媒体ガラス基板用ガラスブランクの製造方法。 - 請求項40~43のいずれか一つに記載の製造方法により前記磁気記録媒体ガラス基板用ガラスブランクを作製し、前記磁気記録媒体ガラス基板用ガラスブランクを加工して磁気記録媒体ガラス基板を作製することを特徴とする磁気記録媒体ガラス基板の製造方法。
- 請求項44に記載の製造方法により前記磁気記録媒体ガラス基板を作製し、前記磁気記録媒体ガラス基板上に磁気記録層を形成する磁気記録層形成工程を少なくとも経て、磁気記録媒体を作製することを特徴とする磁気記録媒体の製造方法。
Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
SG2013020136A SG189021A1 (en) | 2010-09-30 | 2011-09-29 | Method of manufacturing glass blank for magnetic recording medium glass substrate, magnetic recording medium glass substrate manufacturing method, magnetic recording medium manufacturing method, and device for manufacturing glass blank for magnetic recording medium glass substrate |
CN2011800462626A CN103155038A (zh) | 2010-09-30 | 2011-09-29 | 磁记录介质玻璃基板用玻璃坯料的制造方法、磁记录介质玻璃基板的制造方法、磁记录介质的制造方法、以及磁记录介质玻璃基板用玻璃坯料的制造装置 |
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP2010-221316 | 2010-09-30 | ||
JP2010221316A JP5559651B2 (ja) | 2010-09-30 | 2010-09-30 | 磁気記録媒体ガラス基板用ガラスブランク製造方法、磁気記録媒体ガラス基板製造方法、および、磁気記録媒体製造方法 |
JP2010253791A JP5476276B2 (ja) | 2010-11-12 | 2010-11-12 | 磁気記録媒体ガラス基板用ガラスブランクの製造方法、磁気記録媒体ガラス基板製造方法、磁気記録媒体製造方法、磁気記録媒体ガラス基板用ガラスブランクの製造装置 |
JP2010-253791 | 2010-11-12 |
Publications (1)
Publication Number | Publication Date |
---|---|
WO2012043704A1 true WO2012043704A1 (ja) | 2012-04-05 |
Family
ID=45893143
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/JP2011/072337 WO2012043704A1 (ja) | 2010-09-30 | 2011-09-29 | 磁気記録媒体ガラス基板用ガラスブランク製造方法、磁気記録媒体ガラス基板製造方法、磁気記録媒体製造方法、および、磁気記録媒体ガラス基板用ガラスブランクの製造装置 |
Country Status (4)
Country | Link |
---|---|
CN (1) | CN103155038A (ja) |
MY (1) | MY163557A (ja) |
SG (1) | SG189021A1 (ja) |
WO (1) | WO2012043704A1 (ja) |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2014051053A1 (ja) * | 2012-09-28 | 2014-04-03 | Hoya株式会社 | 磁気ディスク用ガラスブランクの製造方法、磁気ディスク用ガラス基板の製造方法、及び磁気ディスク用ガラスブランク |
WO2014163061A1 (ja) * | 2013-03-30 | 2014-10-09 | Hoya株式会社 | 磁気ディスク用ガラス基板の製造方法、磁気ディスク用ガラス基板、及び磁気ディスクの製造方法 |
CN105583720A (zh) * | 2014-11-06 | 2016-05-18 | 株式会社迪思科 | SiC基板的研磨方法 |
Citations (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPH01148717A (ja) * | 1987-12-07 | 1989-06-12 | Canon Inc | 光学素子の成形装置 |
JP2003128425A (ja) * | 2001-10-17 | 2003-05-08 | Fuji Electric Co Ltd | ガラス基板のプレス成形装置及びプレス成形方法 |
JP2004059355A (ja) * | 2002-07-26 | 2004-02-26 | Hoya Corp | ガラスブランク、情報記録媒体用基板および情報記録媒体それぞれの製造方法 |
JP2005263574A (ja) * | 2004-03-19 | 2005-09-29 | Konica Minolta Opto Inc | 情報記録媒体用ガラス基板の製造方法 |
JP2008174401A (ja) * | 2007-01-16 | 2008-07-31 | Konica Minolta Opto Inc | ガラス基板成形用金型、ガラス基板の製造方法、情報記録媒体用ガラス基板の製造方法及び情報記録媒体の製造方法 |
JP2009149477A (ja) * | 2007-12-21 | 2009-07-09 | Hoya Corp | 肉薄ガラスの製造方法、ガラス成形品の製造装置、情報記録媒体用ガラス基板の製造方法、光学部品の製造方法 |
Family Cites Families (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US7395679B2 (en) * | 2004-03-19 | 2008-07-08 | Konica Minolta Opto, Inc. | Method of manufacturing glass substrate for information recording medium |
CN101588996B (zh) * | 2007-01-16 | 2012-02-22 | 柯尼卡美能达精密光学株式会社 | 玻璃基板成型用模具、玻璃基板的制造方法、信息记录介质玻璃基板的制造方法及信息记录介质的制造方法 |
-
2011
- 2011-09-29 MY MYPI2013000582A patent/MY163557A/en unknown
- 2011-09-29 WO PCT/JP2011/072337 patent/WO2012043704A1/ja active Application Filing
- 2011-09-29 CN CN2011800462626A patent/CN103155038A/zh active Pending
- 2011-09-29 SG SG2013020136A patent/SG189021A1/en unknown
Patent Citations (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPH01148717A (ja) * | 1987-12-07 | 1989-06-12 | Canon Inc | 光学素子の成形装置 |
JP2003128425A (ja) * | 2001-10-17 | 2003-05-08 | Fuji Electric Co Ltd | ガラス基板のプレス成形装置及びプレス成形方法 |
JP2004059355A (ja) * | 2002-07-26 | 2004-02-26 | Hoya Corp | ガラスブランク、情報記録媒体用基板および情報記録媒体それぞれの製造方法 |
JP2005263574A (ja) * | 2004-03-19 | 2005-09-29 | Konica Minolta Opto Inc | 情報記録媒体用ガラス基板の製造方法 |
JP2008174401A (ja) * | 2007-01-16 | 2008-07-31 | Konica Minolta Opto Inc | ガラス基板成形用金型、ガラス基板の製造方法、情報記録媒体用ガラス基板の製造方法及び情報記録媒体の製造方法 |
JP2009149477A (ja) * | 2007-12-21 | 2009-07-09 | Hoya Corp | 肉薄ガラスの製造方法、ガラス成形品の製造装置、情報記録媒体用ガラス基板の製造方法、光学部品の製造方法 |
Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2014051053A1 (ja) * | 2012-09-28 | 2014-04-03 | Hoya株式会社 | 磁気ディスク用ガラスブランクの製造方法、磁気ディスク用ガラス基板の製造方法、及び磁気ディスク用ガラスブランク |
WO2014163061A1 (ja) * | 2013-03-30 | 2014-10-09 | Hoya株式会社 | 磁気ディスク用ガラス基板の製造方法、磁気ディスク用ガラス基板、及び磁気ディスクの製造方法 |
JPWO2014163061A1 (ja) * | 2013-03-30 | 2017-02-16 | Hoya株式会社 | 磁気ディスク用ガラス基板の製造方法、磁気ディスク用ガラス基板、及び磁気ディスクの製造方法 |
CN105583720A (zh) * | 2014-11-06 | 2016-05-18 | 株式会社迪思科 | SiC基板的研磨方法 |
Also Published As
Publication number | Publication date |
---|---|
SG189021A1 (en) | 2013-05-31 |
CN103155038A (zh) | 2013-06-12 |
MY163557A (en) | 2017-09-29 |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
JP5662423B2 (ja) | 磁気記録媒体ガラス基板用ガラスブランクの製造方法、磁気記録媒体ガラス基板の製造方法および磁気記録媒体の製造方法 | |
JP6259022B2 (ja) | ガラスブランク | |
JP6234522B2 (ja) | 磁気ディスク用ガラス基板の製造方法 | |
JP6148388B2 (ja) | 磁気ディスク用ガラスブランクの製造方法 | |
JPWO2013001841A1 (ja) | 磁気ディスク用ガラス基板及びその製造方法 | |
US20120247155A1 (en) | Method of manufacturing glass blank for magnetic recording medium glass substrate, method of manufacturing magnetic recording medium glass substrate, method of manufacturing magnetic recording medium, and apparatus for manufacturing glass blank for magnetic recording medium glass substrate | |
JP2012230748A (ja) | 磁気ディスク用ガラス基板の製造方法 | |
US8567216B2 (en) | Manufacturing method of a sheet glass material for magnetic disk, manufacturing method of a glass substrate for magnetic disk | |
WO2012043704A1 (ja) | 磁気記録媒体ガラス基板用ガラスブランク製造方法、磁気記録媒体ガラス基板製造方法、磁気記録媒体製造方法、および、磁気記録媒体ガラス基板用ガラスブランクの製造装置 | |
US8844320B2 (en) | Manufacturing method of a sheet glass material for magnetic disk and manufacturing method of a glass substrate for magnetic disk | |
US8800320B2 (en) | Manufacturing method of a sheet glass material for magnetic disk and manufacturing method of a glass substrate for magnetic disk | |
JP5559651B2 (ja) | 磁気記録媒体ガラス基板用ガラスブランク製造方法、磁気記録媒体ガラス基板製造方法、および、磁気記録媒体製造方法 | |
JP5476276B2 (ja) | 磁気記録媒体ガラス基板用ガラスブランクの製造方法、磁気記録媒体ガラス基板製造方法、磁気記録媒体製造方法、磁気記録媒体ガラス基板用ガラスブランクの製造装置 | |
WO2012111092A1 (ja) | 情報記録媒体基板用ガラスブランク、情報記録媒体用基板及び情報記録媒体の製造方法並びに情報記録媒体基板用ガラスブランク製造装置 | |
JP5330307B2 (ja) | ガラスブランクの製造方法、磁気記録媒体基板の製造方法および磁気記録媒体の製造方法 | |
JP6198780B2 (ja) | 磁気ディスク用ガラスブランク及び磁気ディスク用ガラスブランクの製造方法 | |
JP5306855B2 (ja) | 情報記録媒体用基板の製造方法、および、情報記録媒体の製造方法 | |
WO2013147149A1 (ja) | 磁気ディスク用ガラスブランクの製造方法および磁気ディスク用ガラス基板の製造方法 | |
JP6078414B2 (ja) | 磁気ディスク用ガラスブランクの製造方法及び磁気ディスク用ガラス基板の製造方法 | |
JP2013209262A (ja) | 磁気ディスク用ガラスブランクの製造方法および磁気ディスク用ガラス基板の製造方法 | |
JP2012158513A (ja) | 磁気ディスク用ガラス基板の製造方法 | |
JP2013077366A (ja) | 磁気ディスク用ガラス基板の製造方法 |
Legal Events
Date | Code | Title | Description |
---|---|---|---|
WWE | Wipo information: entry into national phase |
Ref document number: 201180046262.6 Country of ref document: CN |
|
121 | Ep: the epo has been informed by wipo that ep was designated in this application |
Ref document number: 11829257 Country of ref document: EP Kind code of ref document: A1 |
|
WWE | Wipo information: entry into national phase |
Ref document number: 12013500463 Country of ref document: PH |
|
NENP | Non-entry into the national phase |
Ref country code: DE |
|
122 | Ep: pct application non-entry in european phase |
Ref document number: 11829257 Country of ref document: EP Kind code of ref document: A1 |