Glass substrate for magnetic disk and manufacturing method of the same

A method of manufacturing a glass substrate for a magnetic disk, wherein the glass contains in expression of percent by mass:

• SiO2 57 to 75%;
• Al2O3 5 to 20%;
• (where the total amount of SiO2+Al2O3 is 74% or more) the total of ZrO2, HfO2, Nb2O5, Ta2O5, La2O3, Y2O3, and TiO2 exceeding 0% to 6% or less;
• Li2O exceeding 1% to 9% or less;
• Na2O 5 to 18%;
• where the mass ratio Li2O/Na2O is 0.5 or less,
• K2O 0 to 6%;
• MgO 0 to 4%;
• CaO exceeding 0% to 5% or less;
• where the total amount of MgO and CaO is 5% or less, and the content of CaO is higher than the content of MgO, and
• SrO+BaO 0 to 3%,
• said method comprising:
• a chemical reinforcement treatment step of immersing a disk-shaped glass substrate, having a circular hole formed at a center portion thereof and made from said glass, in a chemical reinforcement treatment solution, causing ion exchange for replacing relatively small ions contained in a surface of the glass substrate made from said glass with relatively large ions contained in the chemical reinforcement treatment solution, and thereby creating a compressive stress layer in the surface of the glass substrate,
• wherein the chemical reinforcement treatment is performed so that a deformation amount of the circular hole formed at the center portion of the disk-shaped glass substrate is within 0.05% of the diameter of the circular hole, and that the transverse strength of the disk-shaped glass substrate is 98 N or more.

A method of manufacturing a glass substrate for a magnetic disk, wherein the glass contains in expression of percent by mass:

• SiO2 57 to 75%;
• Al2O3 5 to 20%;
• (where the total amount of SiO2+Al2O3 is 74% or more) the total of ZrO2, HfO2, Nb2O5, Ta2O5, La2O3, Y2O3, and TiO2 exceeding 0% to 6% or less;
• Li2O exceeding 1% to 9% or less;
• Na2O 5 to 18%;
• where the mass ratio Li2O/Na2O is 0.5 or less,
• K2O 0 to 6%;
• MgO 0 to 4%;
• CaO exceeding 0% to 5% or less;
• where the total amount of MgO and CaO is 5% or less, and the content of CaO is higher than the content of MgO, and
• SrO+BaO 0 to 3%,
• wherein the glass substrate is a doughnut-shaped glass substrate for a magnetic disk, and has a circular hole at a center portion thereof, and
• wherein when diameters of circular holes of 500 to 1000 glass substrates that are arbitrarily selected are measured, the diameter of the circular hole of each of the glass substrates is within the range of ±5×10−4×A relative to the average diameter A of the circular holes of the glass substrates, the transverse strength of each of the glass substrates is 98 N or more, and control is thus performed.

A method of manufacturing a glass substrate for a magnetic disk, wherein a glass material in said substrate contains in expression of percent by mass:

• SiO2 57 to 75%;
• Al2O3 5 to 20%;
• where the total amount of SiO2+Al2O3 is 74% or more,
• the total of ZrO2, HfO2, Nb2O5, Ta2O5, La2O3, Y2O3, and TiO2 exceeding 0% to 6% or less;
• Li2O exceeding 1% to 9% or less;
• Na2O 5 to 18%;
• where the mass ratio Li2O/Na2O is 0.5 or less,
• K2O 0 to 6%;
• MgO 0 to 4%;
• CaO exceeding 0% to 5% or less;
• where the total amount of MgO and CaO is 5% or less, and the content of CaO is higher than the content of MgO, and
• SrO+BaO 0 to 3%,
• said method comprising:
• a chemical reinforcement treatment step of immersing a disk-shaped glass substrate with, having a circular hole formed at a center portion thereof and made from said glass material, in a chemical reinforcement treatment solution, causing ion exchange for replacing relatively small ions contained in a surface of the glass substrate made from said glass material with relatively large ions contained in the chemical reinforcement treatment solution, and thereby creating a compressive stress layer in the surface of the glass substrate,
• wherein the chemical reinforcement treatment is performed by selecting said glass material of the disk-shaped glass substrate and treatment conditions of the chemical reinforcement treatment so that a deformation amount of the circular hole formed at the center portion of the disk-shaped glass substrate is within 0.05% of the diameter of the circular hole, and that the transverse strength of the disk-shaped glass substrate is 98 N or more.

A method of manufacturing a glass substrate for a magnetic disk, wherein a glass material in said substrate contains in expression of percent by mass:

• SiO2 57 to 75%;
• Al2O3 5 to 20%;
• where the total amount of SiO2+Al2O3 is 74% or more,
• the total of ZrO2, HfO2, Nb2O5, Ta2O5, La2O3, Y2O3, and TiO2 exceeding 0% to 6% or less;
• Li2O exceeding 1% to 9% or less;
• Na2O 5 to 18%;
• where the mass ratio Li2O/Na2O is 0.5 or less,
• K2O 0 to 6%;
• MgO 0 to 4%;
• CaO exceeding 0% to 5% or less;
• where the total amount of MgO and CaO is 5% or less, and the content of CaO is higher than the content of MgO, and
• SrO+BaO 0 to 3%,
• said method comprising:
• a chemical reinforcement treatment step of immersing a disk-shaped glass substrate, having a circular hole formed at a center portion thereof and made from said glass material, in a chemical reinforcement treatment solution, causing ion exchange for replacing relatively small ions contained in a surface of the glass substrate made from said glass material with relatively large ions contained in the chemical reinforcement treatment solution, and thereby creating a compressive stress layer in the surface of the glass substrate,
• wherein a deformation amount due to the chemical reinforcement treatment of the circular hole formed at the center portion of the disk-shaped glass substrate is beforehand grasped for each glass, said glass material is selected so that the deformation amount is within 0.05% of the diameter of the circular hole, and that the transverse strength of the disk-shaped glass substrate due to the chemical reinforcement treatment is 98 N or more, the selected glass material is processed in disk form, while the circular hole is formed at the center portion, and the chemical reinforcement treatment is performed.