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

A method of manufacturing a magnetic recording medium glass substrate, comprising at least:

• manufacturing a glass blank for a magnetic recording medium glass substrate, comprising at least:
• a first pressing step of pressing a falling molten glass gob with a first press mold and a second press mold placed so as to be opposed to each other in a direction crossing a direction in which the molten glass gob falls to form the falling molten glass gob into a plate shape;
• a second pressing step of continuing to press, with the first press mold and the second press mold, plate glass formed between the first press mold and the second press mold;
• and
• a taking out step of, after the second pressing step, moving the first press mold and the second press mold away from each other and taking out the plate glass sandwiched between the first press mold and the second press mold;
• and
• after that, a polishing step of polishing main surfaces of the glass blank for a magnetic recording medium glass substrate, wherein:
• at least during a period in which the first pressing step and the second pressing step are carried out, the temperature of a press-molding surface of the first press mold and the temperature of a press-molding surface of the second press mold are substantially the same;
• in the first pressing step, the molten glass gob 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 gob substantially at the same time;
• and
• the duration time of the second pressing step is controlled so that the flatness of the glass blank for a magnetic recording medium glass substrate is 10 μm or less.

A method of manufacturing a magnetic recording medium, comprising at least:

• manufacturing a glass blank for a magnetic recording medium glass substrate, comprising at least:
• a first pressing step of pressing a falling molten glass gob with a first press mold and a second press mold placed so as to be opposed to each other in a direction crossing a direction in which the molten glass gob falls to form the falling molten glass gob into a plate shape;
• a second pressing step of continuing to press, with the first press mold and the second press mold, plate glass formed between the first press mold and the second press mold;
• and
• a taking out step of, after the second pressing step, moving the first press mold and the second press mold away from each other and taking out the plate glass sandwiched between the first press mold and the second press mold;
• after that, manufacturing a magnetic recording medium glass substrate, comprising at least a polishing step of polishing main surfaces of the glass blank for a magnetic recording medium glass substrate;
• and further,
• manufacturing a magnetic recording medium, comprising at least a magnetic recording layer-forming step of forming a magnetic recording layer on the magnetic recording medium glass substrate, wherein:
• at least during a period in which the first pressing step and the second pressing step are carried out, the temperature of a press-molding surface of the first press mold and the temperature of a press-molding surface of the second press mold are substantially the same;
• in the first pressing step, the molten glass gob 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 gob substantially at the same time;
• and
• the duration time of the second pressing step is controlled so that the flatness of the glass blank for a magnetic recording medium glass substrate is 10 μm or less.

A method of manufacturing a glass blank for a magnetic recording medium glass substrate, comprising at least a press-molding step of press-molding a falling molten glass gob with a first press mold and a second press mold placed so as to be opposed to each other in a direction crossing a direction in which the molten glass gob falls, wherein:

• at least the first press mold at least comprises:
• a press mold body having a press-molding surface;
• and
• a guide member having at least the function of maintaining a substantially fixed distance between the press-molding surfaces of the first press mold and the second press mold in the press molding, by, when pushed to the side of the second press mold which is placed so as to be opposed to the press-molding surface, being brought into contact with a part of the second press mold which is placed so as to be opposed to the press-molding surface;
• and
• the press-molding step comprises:
• a first step of forming the molten glass gob into plate glass by bringing the first press mold and the second press mold closer together until the guide member of the first press mold and the second press mold are in contact with each other;
• and
• a second step of continuing to press, with the press mold body of the first press mold and the second press mold, the plate glass with the guide member of the first press mold and the second press mold being in contact with each other.

A method of manufacturing a magnetic recording medium glass substrate, comprising at least:

• manufacturing a glass blank for a magnetic recording medium glass substrate, comprising at least a press-molding step of press-molding a falling molten glass gob with a first press mold and a second press mold placed so as to be opposed to each other in a direction crossing a direction in which the molten glass gob falls;
• and
• after that, a polishing step of polishing main surfaces of the glass blank for a magnetic recording medium glass substrate, wherein:
• at least the first press mold at least comprises:
• a press mold body having a press-molding surface;
• and
• a guide member having at least the function of maintaining a substantially fixed distance between the press-molding surfaces of the first press mold and the second press mold in the press molding, by, when pushed to the side of the second press mold which is placed so as to be opposed to the press-molding surface, being brought into contact with a part of the second press mold which is placed so as to be opposed to the press-molding surface;
• and
• the press-molding step comprises:
• a first step of forming the molten glass gob into plate glass by bringing the first press mold and the second press mold closer together until the guide member of the first press mold and the second press mold are in contact with each other;
• and
• a second step of continuing to press, with the press mold body of the first press mold and the second press mold, the plate glass with the guide member of the first press mold and the second press mold being in contact with each other.

A method of manufacturing a magnetic recording medium, comprising at least:

• manufacturing a glass blank for a magnetic recording medium glass substrate, comprising at least a press-molding step of press-molding a falling molten glass gob with a first press mold and a second press mold placed so as to be opposed to each other in a direction crossing a direction in which the molten glass gob falls;
• after that, manufacturing a magnetic recording medium glass substrate, comprising at least a polishing step of polishing main surfaces of the glass blank for a magnetic recording medium glass substrate;
• and further,
• manufacturing a magnetic recording medium, comprising at least a magnetic recording layer-forming step of forming a magnetic recording layer on the magnetic recording medium glass substrate, wherein:
• at least the first press mold at least comprises:
• a press mold body having a press-molding surface;
• and
• a guide member having at least the function of maintaining a substantially fixed distance between the press-molding surfaces of the first press mold and the second press mold in the press molding, by, when pushed to the side of the second press mold which is placed so as to be opposed to the press-molding surface, being brought into contact with a part of the second press mold which is placed so as to be opposed to the press-molding surface;
• and
• the press-molding step comprises:
• a first step of forming the molten glass gob into plate glass by bringing the first press mold and the second press mold closer together until the guide member of the first press mold and the second press mold are in contact with each other;
• and
• a second step of continuing to press, with the press mold body of the first press mold and the second press mold, plate glass with the guide member of the first press mold and the second press mold being in contact with each other.