Plastic article or earthenware shaping or treating: apparatus – Means applying electrical or wave energy directly to work – Radiated energy
Reexamination Certificate
1998-05-19
2001-10-30
Nguyen, Nam (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Means applying electrical or wave energy directly to work
Radiated energy
C425S385000, C425S400000, C425S806000, C425S810000, C264S400000, C264S482000, C264S161000
Reexamination Certificate
active
06309204
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a disc substrate of synthetic resin constituting a disc operating as a recording medium for information signals, such as a magnetic disc, an optical disc or a magneto-optical disc, and a method and apparatus for manufacturing the disc substrate. More particularly, it relates to a disc substrate of synthetic resin in which a head is mounted on a floating slider, with the head and the disc being arranged in close proximity to each other for realizing high-density recording/reproduction.
2. Related Art
In a disc, such as an optical disc, magneto-optical disc or a magnetic disc, a disc substrate is used which is molded from a synthetic resin material exhibiting light transmitting performance, such as polycarbonate resin. This disc substrate has an aperture at a mid portion thereof.
Usually, disc substrates are manufactured by injection molding. That is, in manufacturing the substrates, a substrate material, usually synthetic resin, is melted on heating, and injected under elevated pressure into a cavity corresponding in shape to the desired substrate shape. After cooling and curing of the substrate material, it is taken out from the cavity to manufacture the substrate of a desired shape.
Meanwhile, in usual injection molding, the inside of a metal mold is degassed.
However, since there are interstices in the outer and inner portions of the disc substrate molded in the metal mold, the resin is pulled by this degassing into these interstices to form burrs on the outer and inner portions. These burrs are extremely brittle and ready to break under the effect of various operations performed when taking out the disc substrate out of the metal mold. That is, the disc substrate is significantly lowered in strength in the outer and inner portions thereof due to the burrs formed thereon.
Thus, the disc substrate molded by injection molding experiences a problem that if, during transport of the disc substrate during inspection or assembling steps, a hand area of a transporting jig of the outer rim clamp or outer and/or inner rim vacuum handling system is contacted with the burrs on the outer and/or inner rims, these burrs are detached and turned into projection-like defect of the magnetic film thus lowering the quality of the disc substrate.
Moreover, if, after sputtering the magnetic layer on the disc substrate formed of synthetic resin, pressure is applied to the outer or inner rims of the disc substrate, the burrs on these outer or inner rims, if present, are broken and cracked, thus causing exfoliation due to absorbed or adsorbed water to lower the product quality.
The disc substrate formed of resin by injection molding suffers not only from the burrs, but from the so-called honing phenomenon in which the disc substrate is reduced in thickness as the outermost rim thereof is approached, as shown in FIG.
1
. In the hard disc, a floating head is floated by approximately 50 mm relative to the disc surface and is moved substantially radially of the disc. Since the outer rim portion of the disc is of increased recording area and hence the recording area is preferentially set to as close to the outermost rim of the disc for increasing the recording capacity of the disc. Thus, the planar outer rim portion of the disc is desired for preventing the collision between the disc and the floating slider. Therefore, a smaller magnitude of the honing is desirable. In addition, from the convenience in designing the hard disc drive, this honing needs to be suppressed to within a prescribed magnitude. However, the honing tends to exceed the prescribed magnitude if burrs are formed on the disc substrate.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a disc substrate of synthetic resin which is deburred to eliminate defects in appearance and which is of high quality with improved strength in outer and inner rims thereof.
In one aspect, the present invention provides a method for manufacturing a disc substrate including illuminating a laser light beam on at least the outer rim or the inner rim portions of a disc substrate of synthetic resin for at least transiently melting the illuminated portion, in which the disc substrate is such a disc substrate used for signal recording/reproduction by a head having a floating slider.
With the manufacturing method for the disc substrate according to the present invention, the laser light is illuminated on at least the outer or inner rim of the disc substrate for transiently melting the illuminated portion so that burrs produced during molding are removed or are immobilized against accidental removal for improving the strength of the disc substrate.
In another aspect, the present invention provides a apparatus for manufacturing a disc substrate including a worktable adapted for supporting a disc substrate and for being run in rotation, a positioning unit for positioning the disc substrate at a pre-set position on the worktable and a laser light source that is positioned to illuminate the laser light on at least the outer or inner rim portions of the disc substrate supported for rotation by the worktable. The positioning member is preferably inserted into a center opening in the disc substrate for positioning the disc substrate.
In the above-described manufacturing apparatus for the disc substrate according to the present invention, including the positioning unit for positioning the disc substrate on the worktable and the laser light source for illuminating the laser light on the disc substrate, the laser light can be illuminated on the appropriate positions on the disc substrate, so that the burrs on the disc substrate formed during molding can be efficiently removed or immobilized to eliminate defects in appearance to improve strength of the disc substrate.
In yet another aspect, the present invention provides a disc substrate of synthetic resin used for signal recording/reproduction by a head having a floating slider, wherein the disc substrate has a raised portion at an outer rim portion, with the thickness of the disc substrate at the raised portion being thicker than the thickness of the outermost rim of the disc substrate, with the raised portion being 15 &mgr;m or less in height.
With the above-described disc substrate of the present invention, having the raised portion on its outer rim portion, the disc substrate is increased in strength. The raised portion has a height not larger than 15 &mgr;m, so that the honing may be comprised in the allowable range in consideration of the fact that the floating head slider is caused to run radially of the disc from its outer rim portion towards its recording area.
With the manufacturing method for the disc substrate according to the present invention, having a step of illuminating the laser light on at least the outer or inner rim portion of the disc substrate
2
of synthetic resin for transiently melting the illuminated portion, the material of the disc substrate illuminated by the laser light beam is melted to remove burrs formed on the outer and/or inner rim portions of the disc substrate during injection molding so that there may be produced a disc substrate free of defects in appearance and which is also improved in quality and strength. With the manufacturing method for the disc substrate according to the present invention, the laser light is preferably illuminated n the disc substrate surface at an angle of 30° to 45°, in which case the burrs can be removed more efficiently and the disc substrate can be improved further in strength, while the yield in the manufacturing process may also be improved.
With the manufacturing apparatus for the disc substrate according to the present invention, the laser light can be illuminated on the correctly positioned disc substrate, thus enabling the burrs formed after injection molding to be removed efficiently. Moreover, a disc substrate may be provided which is freed of burrs and hence defects in appearance, and which is of high quality by being improved in st
Del Sole Joseph S
Kananen Ronald P.
Nguyen Nam
Rader Fishman & Grauer
Sony Corporation
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