Background of the Invention There has long been available a magnetic disk cartridge comprising a flat case accommodating a magnetic disk that is a flexible magnetic recording medium obtained by forming magnetic material layers on both sides of a flexible disk- shaped base material composed of polyester sheet or the like (called a"floppy disk"). The magnetic disk is rotated within the case to enable magnetic heads to effect magnetic recording on the magnetic material layers. Owing to such advantages as ease of handling and low cost, this magnetic disk cartridge is used as a recording medium mainly for computers.

A center core member is provided at the center portion of the flexible magnetic recording medium in order to support the magnetic recording medium and define its center of rotation. The center core member is engaged and held by a chuck provided at the tip of a rotating spindle of a drive-

side rotating drive means so as transfer the rotational drive force.

In order to secure the required data transfer rate, the rotational speed of this magnetic disk must be increased in proportion as the recording capacity of the magnetic recording medium increases. In addition, the heights of the rapidly rotating magnetic recording medium and the magnetic heads that conduct recording and reproduction (writing and reading) inherently must be strictly maintained in an appropriate relationship to ensure the desired recording and reproduction performance.

Strict maintenance of the positional relationship between the magnetic recording medium and the magnetic heads is difficult however because the magnetic recording medium is flexible and tends to experience surface undulation during rotation. When the recording density is high, moreover, the penetration performance, which enables tracking even if the magnetic recording medium position shifts relative to the magnetic heads, decreases in breadth. The magnetic recording medium is therefore preferably made easily flexible to enhance tracking performance in its relationship to the magnetic heads.

In light of this, one method used to improve penetration performance is to increase the flexibility of the magnetic recording medium by, for example, narrowing the width of the

fastening flange of the center core member so as to reduce the bonding area with the magnetic recording medium and thus lower the restriction that the center core member exerts on the inner peripheral portion of the magnetic recording medium.

When the outer diameter of the fastening flange of the center core member is decreased so as to reduce its bonding width with the magnetic recording medium, however, assembly performance is essentially degraded and good adhesion cannot be obtained because the region of bonding of the magnetic recording medium by an adhesive becomes small.

Specifically, the adhesive tends to protrude beyond the fastening flange owing to the small area for adhesive application. The protruding adhesive is liable to cause trouble by sticking to the assembly jigs or to adhere to the recording region of the magnetic recording medium and affect the magnetic heads. This makes it necessary to avoid protrusion of adhesive from the fastening flange. As inspection for rejecting magnetic disks with protruding adhesive is difficult to conduct visually, product reliability may be degraded.

In view of the foregoing circumstances, an object of the present invention is to provide a magnetic disk that improves penetration performance by narrowing the bonding region between the center core member and the magnetic

recording medium, prevents protrusion of the adhesive and enables inspection for detecting such protrusion to be conducted satisfactorily.

Summary of the Invention For achieving this object, the present invention provides a magnetic disk characterized in that it comprises a disk- shaped flexible magnetic recording medium and a center core member having a fastening flange fastened to the center portion of the magnetic recording medium, the fastening flange of the center core member being formed to have a flat surface portion for bonding to the magnetic recording medium and an outer peripheral inclined portion produced by bending the outer periphery thereof away from a surface of the magnetic recording medium.

The angle of inclination of the outer peripheral inclined portion of the fastening flange is preferably in the range of 1-10 degrees.

In this magnetic disk according to the present invention, since the fastening flange of the center core member for bonding with the inner peripheral portion of the magnetic recording medium is formed with the flat surface portion for bonding and with the outer peripheral inclined portion produced by bending the outer periphery thereof away from the surface of the magnetic recording medium, the bonding region between the magnetic recording medium and the center

core member is narrowed to lower the restriction that the bonding exerts on the magnetic recording medium, thereby increasing the flexibility of magnetic recording medium. As the positional relationship with the magnetic heads can therefore be maintained, the penetration performance is enhanced to enable excellent recording/reproduction performance. Moreover, even if adhesive should protrude to the outer peripheral inclined portion from the flat surface portion for bonding of the fastening flange, the protruding adhesive will be held within the outer peripheral inclined portion and be prevented from protruding to the exterior. In addition, since inspection for protrusion of adhesive to the outer peripheral inclined portion can be conducted with ease, defective products can be easily identified for rejection. Product reliability can therefore be improved.

Brief Description of the Drawings Figure 1 is an exploded perspective view of a magnetic disk that is an embodiment of the present invention.

Figure 2 is an enlarged view of an essential portion of the magnetic disk.

Figure 3 is a perspective view showing inspection in progress.

Preferred Embodiment of the Invention The invention will now be explained in detail based on an embodiment shown in the drawings. Figure 1 is an exploded

perspective view of a magnetic disk that is an embodiment of the present invention and Figure 2 is an enlarged view of an essential portion.

A magnetic disk is composed of a disk-shaped flexible magnetic recording medium 2 and a center core member 3 for rotational driving that is fastened to the center portion of the magnetic recording medium 2.

The magnetic recording medium 2 is made of a flexible base material such as polyethylene terephthalate (PET) that is formed on its opposite sides with magnetic material layers.

It is disk-like with a center hole 2d. The annular region thereof between an outer peripheral portion and an inner peripheral portion constitutes a recording region 2a. The inner and outer edge portions of the recording region 2a are non-recording regions 2b and 2c.

The center core member 3 is produced by punching a prescribed shape from a stock metal plate of stainless steel or other ferromagnetic material, followed by press-forming.

It is constituted of an engaging portion 4 having a disk- shaped bottom surface, a fastening flange 5 extending brim- like from the upper outer periphery, and a upright cylindrical wall-like connecting portion 6 that connects the outer edge of the engaging portion 4 and the inner edge of the fastening flange 5.

The engaging portion 4 is provided with a center hole portion 4a that opens at the rotational center and a drive pin hole portion 4b that opens at a location outward of the center hole portion 4a. It is engaged and rotated by a magnetic engaging portion of a rotating spindle constituting the drive-side rotating drive means (not shown).

The inner peripheral side portion of the fastening flange 5 is formed as a flat surface portion for bonding 5a lying parallel to the engaging portion 4 (perpendicular to the rotational axis). The flat surface portion for bonding 5a is attached to the non-recording region 2b at the inner peripheral portion of the magnetic recording medium 2 by adhesive 7. At the outer peripheral portion of the flat surface portion for bonding 5a is formed an outer peripheral inclined portion 5b bent away from the surface of the magnetic recording medium 2. The angle of inclination of the outer peripheral inclined portion 5b is set to around 1-10 degrees.

The magnetic recording medium 2 and the center core member 3 are assembled by placing the magnetic recording medium 2 flat on a jig with its center aligne, applying a prescribed amount of adhesive 7 to prescribed locations of the undersurface of the flat surface portion for bonding 5a of the fastening flange 5, holding the fastening flange 5 over the magnetic recording medium 2 using a conveyor jig,

lowering the fastening flange 5 onto the magnetic recording medium 2 while aligning their centers, and pressing the flat surface portion for bonding 5a of the fastening flange 5 onto the inner peripheral portion of the magnetic recording medium 2 to effect bonding by the adhesive 7.

In this embodiment, even if adhesive 7 protrudes from the flat surface portion for bonding 5a to the outer peripheral inclined portion 5b when the adhesive 7 is applied to the flat surface portion for bonding 5a of the fastening flange 5 or during bonding to the magnetic recording medium 2 under pressure, the protruding adhesive 7 causes no trouble and can be easily detected by inspection using an optical sensor or the like to enable rejection of defective products.

Figure 3 shows an example of such inspection in progress.

When a portion of the adhesive 7 applied to the flat surface portion for bonding 5a of the fastening flange 5 of the center core member 3 has oozed to the outer peripheral inclined portion 5b, its presence can be easily found by using an optical sensor 10 to inspect the outer peripheral inclined portion 5b as it is being rotated and detecting the protruding adhesive 7a from variation in the amount of reflected light.

The outer diameter of the connecting portion 6 of the center core member 3 is set smaller than the diameter of the center hole 2d of the magnetic recording medium 2 and the

outer diameter of the fastening flange 5 is set smaller than the outer diameter of the non-recording region 2b of the magnetic recording medium 2. For instance, the connecting portion 6 is formed to an outer diameter of 25mm, the flat surface portion for bonding 5a to an outer diameter of 27mm, and outer peripheral inclined portion 5b to an outer diameter of 29mm.

The magnetic disk is, for example, encased to be capable of rotation in a flat case constituted by bonding together upper and lower shells made of synthetic resin. The case is formed with openings for insertion of magnetic heads and the center portion of the lower shell thereof is formed with a circular hub hole of a size allowing exposure of the engaging portion of the center core member therethrough.