Glass manufacturing – Processes – With wearing away of surface material
Reexamination Certificate
2000-10-02
2003-09-09
Colaianni, Michael (Department: 1731)
Glass manufacturing
Processes
With wearing away of surface material
C451S027000, C451S041000, C451S043000, C451S044000, C451S120000, C451S121000, C451S254000, C451S257000, C451S532000, C451S916000
Reexamination Certificate
active
06615613
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method of grinding a side end surface of a substrate, such as a glass substrate for a magnetic recording medium, and, in particular, to the method suitable for grinding an inner peripheral side end surface and an outer peripheral side end surface of the glass substrate. The inner and the outer peripheral side end surfaces might be simply called inner and outer side end surfaces, respectively, hereinafter. In addition, it should be noted throughout the instant specification that the terms “grind”, “grinding” and “ground” will be used to process the side end surface and to distinguish the end surface processing from the any other processing, especially, main surface processing, but they should be practically interpreted as the meaning of “polish”, “polishing”, and “polished”, respectively.
In general, an aluminum substrate has been widely used as a magnetic recording medium substrate for a magnetic disk or the like. However, it has been a recent trend that such an aluminum substrate has been gradually replaced by a glass substrate which is excellent in flatness and strength in comparison with the aluminum substrate, as the magnetic disk becomes smaller in size, thinner in thickness, and higher in recording density.
As such a glass substrate for the magnetic recording medium, use has been made of a chemically reinforced glass substrate and a crystallized or devitrified glass substrate reinforced by recrystallization or devitrification.
As the recording density becomes higher, a magnetic head has also been changed from a thin film head to a MR (magneto-resistive) head or a GMR (giant magneto-resistive) head. From this fact, it will be expected that the current of times will be directed to reproducing on the magnetic recording medium of the glass substrate by using the magneto-resistive (MR) head.
Under the circumstances, a wide variety of improvements have been made in the magnetic disk so as to realize a high recording density. With such improvements of the magnetic disk, various new problems have taken place one after another in connection with the glass substrate for the magnetic recording medium (will be simply called a glass substrate hereinafter), also. One of the problems is that a substrate surface of the glass substrate must be kept thoroughly clean. For example, when foreign materials are adhered to the substrate surface, they bring about film defects of films deposited on the substrate surface and/or cause projections to occur on the films. In addition, the projections on the films make it difficult to maintain an appropriate glide height.
On the other hand, when the magneto-resistive (MR) head is used for reproducing from the magnetic recording medium of the glass substrate a flying height of the MR head tends to be lowered to improve a recording density. In this event, it often happens that phenomena take place such that reproduction is disordered or becomes impossible. It has been pointed out that the cause or source of the phenomena reside in projections formed by particles adhered to the substrate surface of the glass substrate. Specifically, the projections on the magnetic recording medium give rise to thermal asperity and bring about a temperature rise on the MR head. Such a temperature rise on the MR head results in varying a resistance value of the MR head and adversely affects electro-magnetic conversion.
Now, it is well known that the glass substrate for the magnetic recording medium is shaped like in a ring and, therefore, has an inner side end surface and an outer side end surface which may be referred to as inner and outer side peripheral surfaces, respectively. In addition, the magnetic recording medium is usually housed in a resin case.
As the source of the foreign materials on the glass substrate, recent attention has been directed to particles that occur due to undulations of the side end surfaces of the glass substrate. Specifically, when the magnetic recording medium with the glass substrate is rotated in the resin case, the outer side end surface of the glass substrate rubs a wall of the resin case on account of the undulations of the outer side end surface of the glass substrate. Such rubbing brings about adhesion of the particles or resin, glass, and the like to the magnetic recording medium. Moreover, any other particles are often adhered to the magnetic recording medium from the inner and the outer side end surfaces of the glass substrate.
Especially, it has been found out by the instant inventors that the inner side end surface of the glass substrate is rough or equivalent in flatness as compared with the outer side end surface and is therefore susceptible to cause undesired particles.
As regards a chemically reinforced glass substrate as mentioned before, chemical reinforcement is carried out by immersing a glass substrate into a chemical reinforcement or strengthening solution that is heated. On immersion, the glass substrate itself is held in a holder (for example, three points holder). Specifically, a plurality of the glass substrates are supported by the holder at support portions of the outer end side surface of the glass substrates. Herein, it is assumed that the outer end side surfaces of the glass substrates are not flat especially at the support portions. In this case, undesired liquid sumps of the chemical reinforcement solution are liable to occur at the support portions when the glass substrates are lifted from the chemical reinforcement solution .Such liquid sumps leave, on the support portions, particles resulting from foreign materials included in the chemical reinforcement solution and finally result in occurrence of the thermal asperity due to the particles.
Conventionally, a method and an apparatus for grinding inner and outer side end surfaces of a glass substrate are disclosed in Japanese Patent Unexamined Publication Nos. H11-33886 (33886/1999) and H11-28649 (28649/1999). In each conventional grinding method, a plurality of glass substrates or glass disks are stacked on a rotatable table and are rotated in a predetermined direction. Grinding is performed by supplying the rotating glass substrates with slurry including an abrasive material and by rotating a grinding brush in a direction reverse relative to the predetermined direction of the glass substrates. Furthermore, the grinding brush is reciprocated in a stacked direction of the glass substrates. Thus, the inner and outer side end surfaces can be ground.
Such grinding the side end surfaces is generally performed with the glass substrates directly stacked together before the glass substrates are chemically reinforced. This shows that un-reinforced or pre-reinforced glass substrates are ground by the grinding brush with a pressure imposed onto the side end surfaces of the glass substrates by the grinding brush. As a result, the pressure of the grinding brush is directly given to the glass substrates stacked one another and often brings about breakage of the glass substrates. In order to avoid the breakage of the glass substrates, the grinding of the side end surfaces (may be called side surface grinding) must be performed when each glass substrate is thick to some extent. Taking this into consideration, the side surface grinding is usually carried out before a final lapping process for lapping or polishing each glass substrate by the use of a carrier including abrasive grains.
Herein, let the final lapping process be carried out after the side surface grinding. In this event, each glass substrate is lapped or rubbed during the final lapping process not only on a main surface thereof but also on the side end surface. This is because the abrasive gains undesirably lap or rub the side surfaces of each glass substrate due to an interference between the abrasive material used in the side surface grinding and the abrasive grains used in the final lapping process.
Since the side end surfaces are once mirror finished by the side surface grinding, the side end surfaces are roughened again by the abrasive grains during the
Iwabuchi Shozo
Katagiri Masahiro
Colaianni Michael
Hoya Corporation
Sughrue & Mion, PLLC
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