Toyo Kohan Co., Ltd.

Gen Ishida

Takahiro Yoshida

Nobuaki Mukai

Hiroshi Doi

Yoshio Uchiyama

An object of the present invention is to obtain a hard disk substrate that can have a smooth surface of a plating film through electroless NiP plating and does not have deteriorated corrosion resistance against acid solutions. A method for producing a hard disk substrate of the present invention is a method for producing a hard disk substrate with an electroless NiP plating film, the method including immersing a substrate in a first electroless NiP plating bath containing an additive with leveling action, thereby forming a lower layer of the electroless NiP plating film on a surface of the substrate, the lower layer having smaller average surface roughness than the surface; and immersing the substrate that has the lower layer of the electroless NiP plating film formed thereon through the first plating step in a second electroless NiP plating bath, thereby forming an upper layer of the electroless NiP plating film, the upper layer having corrosion resistance against acid solutions and having a thickness of greater than or equal to 4 &#x3bc;m.

Method for producing hard disk substrate

An inner peripheral edge of a toroidal glass substrate for a magnetic disk is subjected to mechanical polishing in such a manner that the surface roughness is no greater than 9 nm in terms of Rmax. Then, the inner peripheral edge is subjected to chemical polishing to remove at least 2 &#x3bc;m of a surface layer. The inner peripheral edge has a non-conventional mirror-finished surface obtained by mechanical polishing. Thus, sufficient ring strength is obtained even when the chemical polishing depth is smaller than in the past. A polishing depth of less than 5 &#x3bc;m is sufficient.

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Yamaguchi, Japan

Gen Ishida