GLASS SUBSTRATE FOR A MAGNETIC DISK AND MAGNETIC DISK

• Main Authors: MAEDA, TAKASHI, EDA, SHINJI, TSUCHIYA, HIROSHI, ISONO, HIDEKI, MARUMO, YOSHINORI
• Format: Patent
• Language: English
• Published: 29.11.2013

GLASS SUBSTRATE FOR A MAGNETIC DISK AND MAGNE C DISKProvided are a magnetic disc substrate and a method for manufacturing the sam magnetic disc substrate has significantly few defects existing on the front s . level in the vicinity of 0.1.nm of an arithmetic average roughness (Ra) and : density recording magnetic disc substrate. The magnetic disc glass substr the arithnietic mean roughness (Ra) on the main front surface of the gl less at a square of 2 Imulm 2 [mu]m measured by using an atomic fo resolution of 256 256 pixels. The magnetic disc glass substrate is a number of defects which are detected to be 0.1 [mu]m - 0.6 [mu nm - 2 mu in depth, as detected by using a deviation of wavelen reflective light in the case where helium neon laser light of th , while the laser light is being irradiated to the main front s 10 per 24 cm2.The method of manufacturing a magnetic disc glass s polishing step where a polishing liquid containingcleaning liquid also containing the additive is use acid, polyvalent amine, amino acid, amino polyc phosphoric acid, pyrophosphoric acid, tripolyp or their salts. Figure 1 GLASS SUBSTRATE FOR A MAGNETIC DISK AND MAGNETIC DISK* *ProVided are d magnetic disc stibatiate and a inetliod for manufacturing the same, wherein a magnetic disc substrate has significantly few defects existing on the front surface thereof at the level in the vicinity of 0.1'nm of an.arithmetic average roughness *(Ra) and is suitable for.a high .: density recording magnetic disc substrate. The magnetic disc glass substrate is characterized in that the arithrnetic mean roughness (Ra) on theMain front surface of the glass substrate is 0.12 mu or less at a square of 2 Imu]m 2 [mu]m measured by using an atomic force microscope with the resolution of 256 256 pixels. The magnetic disc glass substrate is also characterized in that the number of defects which are detected to be 0.1 [mu]m - 0.6 [mujni in size from a plan view and 0.5 nm - 2 mu in depth, as detected by using a deviation of wavelengths between incident light and reflective light in the case where helium neon laser light of the wavelength of 632 run is swept: while the laser light is being irradiated to the main front surface of the glass substrate, is less than 10 per 24 cm2.The method of manufacturing a magnetic disc glass substrate is characterized in cOmprising a polishing step where a polishing liquid containing an additive is used, and a cleaning step where a cleaning liquid also containing the additive is used. Examples of the additive includes: carboxylic acid, polyvalent amine, amino acid, amino polycarboxylic acid, phosphonic aeid, phosphinic acid, phosphoric acid, pyrophosphoric acid, tripolyphosphoric acid, amino trirnethylene phosphoric acid; or their salts. Figure 1