Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
2000-07-28
2001-04-17
Resan, Steven A. (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C428S065100, C428S066700, C428S690000, C428S690000, C428S900000, C428S426000, C428S432000
Reexamination Certificate
active
06217980
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a magnetic recording medium used for a computer and the like.
Heretofore, an aluminum substrate has been widely used for a magnetic recording medium, such as a magnetic disk. However, the aluminum substrate has been gradually replaced by a glass substrate which is advantageous in strength and flatness as compared with the aluminum substrate.
On the other hand, a thin-film head has been widely used as a magnetic head. However, the thin-film head tends to be recently replaced by a magneto-resistive head (MR head) and a giant magneto-resistive head (GMR head). Therefore, development would be directed to a magnetic recording medium which can be matched with the magneto-resistive head. Such a magnetic recording medium often has a glass substrate.
However, reproduction errors very often occur and a reproduction becomes more difficult as a flying height becomes lower when the magneto-resistive head runs along the magnetic recording medium of the glass substrate.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a magnetic recording medium which is capable of reducing a reproduction error even if a flying height of a magnetic head becomes low.
As mentioned above, the reproduction error often occurs when the flying height of the magnetic head becomes low. Therefore, close investigation has been carried out about the cause of the reproduction error. According to the inventors' experimental studies, it is found out that particles are attached on a principal surface of a glass substrate and projections are formed due to the particles on the magnetic recording medium. Such projections bring about a thermal asperity which causes the magneto-resistive head to generate heat. As a result, a resistivity of the head is fluctuated and thereby, an adverse influence is given to electro-magnetic conversion.
Further, the thermal asperity is often generated for the magnetic disk after a glide test for checking a head crash. In this case, various particles bring about the thermal asperity. For example, such particles may include a particle which gives an adverse influence when the head is afloat. Such a particle comprises an angular or irregular configuration.
Subsequently, the cause that the particles are attached to the conventional glass substrate has been investigated. As a result of the investigation, it is found out that the particles generated from a side end surface of the glass substrate are attached to the principal surface of the glass substrate. This is because the end side surface is rough as compared with a principal surface of the glass substrate. Specifically, when the glass substrate is got in and out of a housing of a material such as a polycarbonate, the side end surface of the glass substrate is inevitably contacted with an internal surface of the housing. Such contacts of the side end surface with the housing give rise to generation of the particles and the generated particles are attached on the principal surface of the glass substrate.
Conventionally, an attention has been generally paid for the side end surface only from the viewpoint of a mechanical strength of the glass substrate. In contrast, an attention is paid in U.S. Pat. No. 5,569,518 for avoiding generation of the particles by chemically etching or polishing the side end surface into a chemical polished surface. It is known in the art that such a chemical polished surface is rough and exhibits a mat (or dull) finished surface. As a result, it has been confirmed that the side end surface must be precisely polished by mechanical polishing to avoid generation of the particles. Conventionally, the side end surface is processed by chemical etching. However, the chemical etching process is not enough to suppress generation of the particles.
Herein, it is assumed that a magnetic recording medium which is manufactured by the use of the glass substrate is shaped in a disk which has an inner periphery and an outer periphery. In this event, the inner and the outer peripheries are irregularly etched, which might result in deviation of an axis.
On the other hand, the present invention points out that generation of particles can be prevented by mechanically polishing the side surface into a mirror finished surface without any deviation of an axis in a magnetic recording medium.
Specifically, according to this invention, the glass substrate has a pair of principal surfaces opposite to each other and a peripheral side area contiguous to the principal surfaces. The peripheral side area has a side end wall and intermediate regions between the side end wall and the principal surfaces. In this case, at least one of the intermediate regions and the side end wall is formed by a mirror finished surface which has a surface roughness Ra not greater than 1 &mgr;m or a surface roughness Rmax not greater 4 &mgr;m.
In this invention, no particles are generated because the side end surface of the glass substrate is mirror finished. Consequently, reproducing function is not reduced by the thermal asperity. Further, a head crash can be sufficiently prevented since no projections are formed due the particles on the magnetic recording medium.
REFERENCES:
patent: 5080948 (1992-01-01), Morita et al.
patent: 5128922 (1992-07-01), Inui et al.
patent: 5341606 (1994-08-01), Hirabayashi
patent: 5470694 (1995-11-01), Ohta et al.
patent: 0105374 (1984-04-01), None
Kojima Takeshi
Miyamoto Takemi
Takahashi Kouichi
Hoya Corporation
Resan Steven A.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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