Substrate for magnetic recording media using dried thermoplastic norbornene resin and magnetic recording media using substrate
View Patent ↗The gas components in thermoplastic norbornene resin pellets are suppressed below certain levels by drying the resin under vacuum or under the ordinary pressure and under vacuum. A substrate for magnetic recording media is manufactured by injection-molding the resin dried by the method according to the invention. The magnetic recording medium, employing the substrate manufactured according to the invention, includes at least a magnetic layer, a protection layer on the magnetic layer and a liquid lubricant layer on the protection layer. The magnetic recording medium is manufactured by forming these layers, one after another, on the substrate according to the invention.
1. A plastic substrate for magnetic recording media, said plastic substrate being manufactured by injection molding a thermoplastic norbornene resin dried by a method comprising:
drying said thermoplastic norbornene resin under one of a degree of vacuum of 20 Pa or lower, and a degree of vacuum of 20 Pa or lower and ordinary pressure; wherein
said drying removes atmospheric gas components and low-boiling-point organic components contained in said thermoplastic norbornene resin; and wherein
said thermoplastic norbornene resin contains, after said drying, N 2 of 20 ppm or lower, O 2 of 20 ppm or lower, and H 2 O of 1 ppm or lower.
2. A plastic substrate for magnetic recording media, of claim 1 wherein:
said drying under ordinary pressure is conducted at a temperature between 80 and 120° C.; and
said drying under vacuum is conducted under a degree of vacuum of 20 Pa or lower at a temperature between 80 and 120° C.
3. A plastic substrate for magnetic recording media, of claim 1 wherein:
the thermoplastic norbornene resin contains, low-boiling-point aliphatic organic components of 20 ppb or lower in total, and low-boiling-point aromatic organic components of 20 ppb or lower in total.
4. A plastic substrate for magnetic recording media, of claim 2 wherein:
the thermoplastic norbornene resin contains, after the drying, N 2 of 20 ppm or lower, O 2 of 20 ppm or lower, H 2 O of 1 ppm or lower, low-boiling-point aliphatic organic components of 20 ppb or lower in total, and low-boiling-point aromatic organic components of 20 ppb or lower in total.
5. The plastic substrate according to claim 1 , wherein said plastic substrate contains, in a surface thereof, 100 or less rugged portions of 1 μm×1 μm or wider in area wherein said substrate is 95 mm in diameter.
6. The plastic substrate according to claim 1 , wherein:
a straightness, Pa, in the radial direction of said plastic substrate, is 1 μm or less;
a micro-waviness of said plastic substrate is 500 Åor lower; and
an average surface roughness of said plastic substrate is 5 Åor lower.
7. The plastic substrate according to claim 5 , wherein:
a straightness, Pa, in the radial direction of said plastic substrate, is 1 μm or less;
a micro-waviness of said plastic substrate is 500 Åor lower; and
an average surface roughness of said plastic substrate is 5 Åor lower.
8. A magnetic recording medium comprising:
said plastic substrate according to claim 1 ;
a magnetic layer above said plastic substrate;
a protection layer on said magnetic layer; and
a lubricant layer on said protection layer.
9. The magnetic recording medium according to claim 8 , wherein said plastic substrate contains, in a surface thereof, 100 or less rugged portions of 1 μm×1 μm or wider in area wherein said substrate is 95 mm in diameter.
10. The magnetic recording medium according to claim 8 , wherein:
a straightness, Pa, in the radial direction of said plastic substrate, is 1 μm or less;
a micro-waviness of said plastic substrate is 500 Åor lower; and
an average surface roughness of said plastic substrate is 5 Åor lower.
11. The magnetic recording medium according to claim 9 , wherein:
a straightness, Pa, in the radial direction of said plastic substrate, is 1 μm or less;
a micro-waviness of said plastic substrate is 500 Åor lower; and
an average surface roughness of said plastic substrate is 5 Åor lower.
12. The magnetic recording medium according to claim 8 , wherein an output of a strain gauge is 0.5 g or less at the end of continuous and high-speed head seek tests conducted for 24 hr on said magnetic recording medium, rotating at 4500 rpm using a low-flying-height head having a flying height of 1 μ″;
wherein said output is a measure of resistance between the surface of the head and the surface of the protection layer.