Yamamura Glass Co., Ltd.

E.i. Dupont De Nemours and Company

Nihon Yamamura Glass Co., Ltd.

Ikuo Kuriyama

Tomoyuki Taguchi

Hideki Kawai

Hajimu Wakabayashi

Tohru Ohara

Keiichiro Hayakawa

Hisashi Matsuno

Sadao Nakajima

Ichiro Uchiyama

An object of the present invention is to provide a lead-free bismuth glass wherein decrease of the degree of accuracy of the patterning is prevented. Specifically, the present invention provides a lead-free bismuth glass characterized in that said lead-free bismuth glass is used for an optical patterning glass material which is patterned by light irradiation and the optical-absorption coefficient to light with a wavelength of 365 nm is 300 to 3000 cm.

Lead-free bismuth glass

A glass composition for magnetic disk substrates comprising as oxides: from 66 to 80% by weight of SiO.sub.2, from 5 to 15% by weight of Al.sub.2 O.sub.3, from 3 to 8.5% by weight of Li.sub.2 O, from 0 to 3% by weight of Na.sub.2 O, from 0 to 3% by weight of K.sub.2 O, from 0.5 to 8% by weight of TiO.sub.2, from 3.5 to 8% by weight of ZrO.sub.2, from 0.5 to 3% by weight of P.sub.2 O.sub.5, from 0 to 2% by weight of Sb.sub.2 O.sub.3, and from 0 to 2% by weight of As.sub.2 O.sub.3, and having a theoretical optical basicity of 0.548 or less; a magnetic disk substrate which is prepared by forming and polishing the above glass composition, followed by chemically strengthening the polished substrate by ion exchange or by forming, heat treating, and polishing the above composition and contains Li.sub.2 O.2SiO.sub.2 and/or spodumene as the main crystalline phase. The glass composition for magnetic disk substrates can easily be formed, can easily be polished after crystallization of the glass by heat treatment or chemically strengthened by ion exchange of the glass after forming and polishing, and is used for preparing magnetic disk substrates which has excellent chemical durability, mechanical strength, heat resistance, surface flatness, and surface smoothness, and shows little degradation of magnetic film characteristics by alkali migration.

Magnetic disk substrate

A glass-ceramic magnetic disk substrate which is prepared by forming, then heat treating, and then polishing a crystallizable glass composition comprising, expressed in terms of weight percent on the oxide basis: from 20 to 45% SiO.sub.2 ; from 25 to 45% Al.sub.2 O.sub.3 ; from 10 to 25% B.sub.2 O.sub.3 ; from 2 to 12% MgO; from 0.5 to 8% TiO.sub.2 ; from 0.5 to 5% P.sub.2 O.sub.5 ; from 0 to 2% Li.sub.2 O; from 0 to 2% Na.sub.2 O; from 0 to 3% K.sub.2 O; wherein, the total of the contents of Li.sub.2 O, Na.sub.2 O and K.sub.2 O is from 0 to 5%; and wherein the magnetic disk substrate comprises a main crystalline phase consisting of at least one member selected from the group consisting of mullite and aluminum borate crystals. The glass composition can easily be formed and the disk substrate can easily be polished, has excellent mechanical strength, surface flatness, surface smoothness, chemical durability, and heat resistance, and shows no deterioration of magnetic film characteristics by alkali migration.

Glass-ceramic magnetic disk substrate

A glass composition for magnetic disk substrates comprising as oxides: from 66 to 80% by weight of SiO.sub.2, from 5 to 15% by weight of Al.sub.2 O.sub.3, from 3 to 8.5% by weight of Li.sub.2 O, from 0 to 3% by weight of Na.sub.2 O, from 0 to 3% by weight of K.sub.2 O, from 0.5 to 8% by weight of TiO.sub.2, from 3.5 to 8% by weight of ZrO.sub.2, from 0.5 to 3% by weight of P.sub.2 O.sub.5, from 0 to 2% by weight of Sb.sub.2 O.sub.3, and from 0 to 2% by weight of As.sub.2 O.sub.3, and having a theoretical optical basicity of 0.548 or less; a magnetic disk substrate which is prepared by forming and polishing the above glass composition, followed by chemically strengthening the polished substrate by ion exchange or by forming, heat treating, and polishing the above composition and contains Li.sub.2 O.multidot.2SiO.sub.2 and/or spodumene as the main crystalline phase. The glass composition for magnetic disk substrates can easily be formed, can easily be polished after crystallization of the glass by heat treatment or chemically strengthened by ion exchange of the glass after forming and polishing, and is used for preparing magnetic disk substrates which has excellent chemical durability, mechanical strength, heat resistance, surface flatness, and surface smoothness, and shows little degradation of magnetic film characteristics by alkali migration.

Glass composition for magnetic disk substrates and magnetic disk

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Hyogo, Japan

Ikuo Kuriyama